Question: When did the country with the most tornadoes in the world take over northern Ireland?

full_context: Document 1: British Empire: In 1919, the frustrations caused by delays to Irish home rule led members of Sinn Féin, a pro-independence party that had won a majority of the Irish seats at Westminster in the 1918 British general election, to establish an Irish assembly in Dublin, at which Irish independence was declared. The Irish Republican Army simultaneously began a guerrilla war against the British administration. The Anglo-Irish War ended in 1921 with a stalemate and the signing of the Anglo-Irish Treaty, creating the Irish Free State, a Dominion within the British Empire, with effective internal independence but still constitutionally linked with the British Crown. Northern Ireland, consisting of six of the 32 Irish counties which had been established as a devolved region under the 1920 Government of Ireland Act, immediately exercised its option under the treaty to retain its existing status within the United Kingdom.
Document 2: North Carolina: North Carolina averages fewer than 20 tornadoes per year, many of them produced by hurricanes or tropical storms along the coastal plain. Tornadoes from thunderstorms are a risk, especially in the eastern part of the state. The western Piedmont is often protected by the mountains, which tend to break up storms as they try to cross over; the storms will often re-form farther east. Also a weather phenomenon known as "cold air damming" often occurs in the northwestern part of the state, which can also weaken storms but can also lead to major ice events in winter.
Document 3: Tornadoes in the United States: Most tornadoes in the United States occur east of the Rocky Mountains. The Great Plains, the Midwest, the Mississippi Valley and the southern United States are all areas that are vulnerable to tornadoes. They are relatively rare west of the Rockies and are also less frequent in the northeastern states. Tornado Alley is a colloquial term for an area particularly prone to tornadoes. There is no officially defined 'Tornado Alley' -- at its broadest this area stretches from North Texas to Canada with its core centered on Oklahoma, Kansas and northern Texas. Another highly significant region -- colloquially known as Dixie Alley -- is the southern United States and particularly the northern and central parts of Alabama and Mississippi. Florida is one of the most tornado prone states. However, Florida tornadoes only rarely approach the strength of those that occur elsewhere.
Document 4: Tornado climatology: The United States has the most tornadoes of any country. Many of these form in an area of the central (with some definitions including Southern) United States known as Tornado Alley. This area extends into Canada, particularly the Prairie Provinces and Ontario; however, activity in Canada is less frequent and intense than that of the US. The high frequency of tornadoes in North America is largely due to geography, as moisture from the Gulf of Mexico is easily advected into the midcontinent with few topographic barriers in the way. The Rocky Mountains block Pacific - sourced moisture and buckle the atmospheric flow, forcing drier air at mid-levels of the troposphere due to downsloping winds and causing cyclogenesis downstream to the east of the mountains. Downsloping winds off the Rockies force the formation of a dry line when the flow aloft is strong, while the Gulf of Mexico fuels abundant low - level moisture. This unique topography allows for frequent collisions of warm and cold air, the conditions that breed strong, long - lived storms throughout the year. This area extends into Canada, particularly Ontario and the Prairie Provinces, and strong tornadoes can also occur in northern Mexico.
Document 5: Northern Ireland: Northern Ireland (Irish: Tuaisceart Éireann (ˈt̪ɣuəʃcəɾɣt̪ɣ ˈeːɾjən̪ɣ) (listen); Ulster - Scots: Norlin Airlann) is a part of the United Kingdom in the north - east of the island of Ireland, variously described as a country, province or region. Northern Ireland shares a border to the south and west with the Republic of Ireland. In 2011, its population was 1,810,863, constituting about 30% of the island's total population and about 3% of the UK's population. Established by the Northern Ireland Act 1998 as part of the Good Friday Agreement, the Northern Ireland Assembly holds responsibility for a range of devolved policy matters, while other areas are reserved for the British government. Northern Ireland co-operates with the Republic of Ireland in some areas, and the Agreement granted the Republic the ability to ``put forward views and proposals ''with`` determined efforts to resolve disagreements between the two governments''.
Document 6: Tornado climatology: The United States averaged 1,274 tornadoes per year in the last decade while Canada reports nearly 100 annually (largely in the southern regions). However, the UK has most tornadoes per area per year, 0.14 per 1000 km2, although these tornadoes are generally weak, and many other European countries have a similar number of tornadoes per area.
Document 7: United Kingdom of Great Britain and Ireland: The United Kingdom of Great Britain and Ireland was established as a sovereign state on 1 January 1801 by the Acts of Union 1800, which merged the kingdoms of Great Britain and Ireland. The growing desire for an Irish Republic led to the Irish War of Independence, which resulted in Ireland seceding from the Union and forming the Irish Free State in 1922. Northern Ireland remained part of the United Kingdom, and the state was consequently renamed the ``United Kingdom of Great Britain and Northern Ireland ''.
Document 8: Tornadoes in the United States: Tornadoes are more common in United States than in any other country. The United States receives more than 1,200 tornadoes annually -- four times the amount seen in Europe. Violent tornadoes -- those rated EF4 or EF5 on the Enhanced Fujita Scale -- occur more often in the United States than in any other country.
Document 9: Tornado climatology: Tornadoes have been recorded on all continents except Antarctica and are most common in the middle latitudes where conditions are often favorable for convective storm development. The United States has the most tornadoes of any country, as well as the strongest and most violent tornadoes. A large portion of these tornadoes form in an area of the central United States popularly known as Tornado Alley. Other areas of the world that have frequent tornadoes include significant portions of Europe, South Africa, Philippines, Bangladesh, parts of Argentina, Uruguay, and southern and southeast Brazil, northern Mexico, New Zealand, and far eastern Asia.
Document 10: Tornado climatology: Tornadoes have been recorded on all continents except Antarctica and are most common in the middle latitudes where conditions are often favorable for convective storm development. The United States has the most tornadoes of any country, as well as the strongest and most violent tornadoes. A large portion of these tornadoes form in an area of the central United States popularly known as Tornado Alley. Other areas of the world that have frequent tornadoes include significant portions of Europe, South Africa, Philippines, Bangladesh, parts of Argentina, Uruguay, and southern and southeast Brazil, New Zealand, and far eastern Asia.
Document 11: History of Ireland: Unwilling to negotiate any understanding with Britain short of complete independence, the Irish Republican Army, the army of the newly declared Irish Republic, waged a guerilla war (the Irish War of Independence) from 1919 to 1921. In the course of the fighting and amid much acrimony, the Fourth Government of Ireland Act 1920 implemented Home Rule while separating the island into what the British government's Act termed ``Northern Ireland ''and`` Southern Ireland''. In July 1921 the Irish and British governments agreed to a truce that halted the war. In December 1921 representatives of both governments signed an Anglo - Irish Treaty. The Irish delegation was led by Arthur Griffith and Michael Collins. This abolished the Irish Republic and created the Irish Free State, a self - governing Dominion of the Commonwealth of Nations in the manner of Canada and Australia. Under the Treaty, Northern Ireland could opt out of the Free State and stay within the United Kingdom: it promptly did so. In 1922 both parliaments ratified the Treaty, formalising independence for the 26 - county Irish Free State (which renamed itself Ireland in 1937, and declared itself a republic in 1949); while the 6 - county Northern Ireland, gaining Home Rule for itself, remained part of the United Kingdom. For most of the next 75 years, each territory was strongly aligned to either Catholic or Protestant ideologies, although this was more marked in the six counties of Northern Ireland.
Document 12: History of Ireland: In 1922, after the Irish War of Independence and the Anglo - Irish Treaty, most of Ireland seceded from the United Kingdom to become the independent Irish Free State, which after the 1937 constitution, began to call itself Ireland. The six northeastern counties, known as Northern Ireland, remained within the United Kingdom. The Irish Civil War followed soon after the War of Independence. The history of Northern Ireland has since been dominated by sporadic sectarian conflict between (mainly Catholic) Irish nationalists and (mainly Protestant) unionists. This conflict erupted into the Troubles in the late 1960s, until peace was achieved with the Belfast Agreement thirty years later.
Document 13: Tornadoes in the United States: Nebraska is fifth overall for sheer numbers of tornadoes, while Indiana has had 88 violent tornado reports from the 1950 -- 2006 period, more than any state except Oklahoma. Iowa reported 3'900 almost as many as Texas. The deadliest tornado in US history, the Tri-State Tornado, struck Missouri, Illinois, and Indiana in March 1925. St. Louis, Missouri and neighboring East St. Louis, Illinois have been hit more than once by violent tornadoes, the most notorious of which was the St. Louis Tornado of May 1896. The New Richmond Tornado of May 1899 and the Flint, Michigan tornado of June 1953 also rank amongst the deadliest tornadoes in US history. The region was badly hit by the Palm Sunday Tornado Outbreak in April 1965 and by the Super Outbreak of April 1974. According to NCDC figures for the 1950 to 2006 period, Nebraska reported 2,440 tornadoes followed by Iowa (2,185), Illinois (2,086), Missouri (1,922), South Dakota (1,487), Minnesota (1,477), Indiana (1,327), North Dakota (1,216), Wisconsin (1,185), Michigan (981), and Ohio (916).
Document 14: British Isles: The Northern Ireland Peace Process has led to a number of unusual arrangements between the Republic of Ireland, Northern Ireland and the United Kingdom. For example, citizens of Northern Ireland are entitled to the choice of Irish or British citizenship or both and the Governments of Ireland and the United Kingdom consult on matters not devolved to the Northern Ireland Executive. The Northern Ireland Executive and the Government of Ireland also meet as the North/South Ministerial Council to develop policies common across the island of Ireland. These arrangements were made following the 1998 Good Friday Agreement.
Document 15: Northern Ireland: Northern Ireland was created in 1921, when Ireland was partitioned between Northern Ireland and Southern Ireland by the Government of Ireland Act 1920. Unlike Southern Ireland, which would become the Irish Free State in 1922, the majority of Northern Ireland's population were unionists, who wanted to remain within the United Kingdom. Most of these were the Protestant descendants of colonists from Great Britain. However, a significant minority, mostly Catholics, were nationalists who wanted a united Ireland independent of British rule. Today, the former generally see themselves as British and the latter generally see themselves as Irish, while a distinct Northern Irish or Ulster identity is claimed both by a large minority of Catholics and Protestants and by many of those who are non-aligned.
ground_truth: 1921
sub_queries: who has the most tornadoes in the world Answer: the UK
when did the the UK take over northern ireland Answer: 1921