Question: When did the border between Ireland and the part of the U.K. that experienced Bloody Friday become a free-travel area?

<P0-S0> the united kingdom of great britain and northern ireland, commonly known as the united kingdom (uk) or britain, is a sovereign country lying off the north - western coast of the european mainland. <P0-S1> the united kingdom includes the island of great britain, the north - eastern part of the island of ireland and many smaller islands. <P0-S2> northern ireland is the only part of the united kingdom that shares a land border with another sovereign state‍ -- ‌the republic of ireland. <P0-S3> apart from this land border, the united kingdom is surrounded by the atlantic ocean, with the north sea to its east, the english channel to its south and the celtic sea to its south - south - west, giving it the 12th - longest coastline in the world. <P0-S4> the irish sea lies between great britain and ireland. <P0-S5> with an area of 242,500 square kilometres (93,600 sq mi), the united kingdom is the 78th - largest sovereign state in the world. <P0-S6> it is also the 22nd-most populous country, with an estimated 66.0 million inhabitants in 2017. <SEP> <P1-S0> CAMRA maintains a "National Inventory" of historical notability and of architecturally and decoratively notable pubs. <P1-S1> The National Trust owns thirty-six public houses of historic interest including the George Inn, Southwark, London and The Crown Liquor Saloon, Belfast, Northern Ireland. <SEP> <P2-S0> At least twenty bombs exploded in the space of eighty minutes, most within a half hour period. <P2-S1> Most of them were car bombs and most targeted infrastructure, especially the transport network. <P2-S2> Nine people were killed: five civilians, two British soldiers, a Royal Ulster Constabulary (RUC) reservist, and an Ulster Defence Association (UDA) member, while 130 were injured. <P2-S3> The IRA said it sent telephoned warnings at least thirty minutes before each explosion and claimed the security forces wilfully ignored some of the warnings for its own ends. <P2-S4> The security forces denied this and said they were overstretched by the sheer number of bombs and bomb warnings, some of which were hoaxes. <P2-S5> Bloody Friday is the name given to the bombings by the Provisional Irish Republican Army (IRA) in Belfast on 21 July 1972, during the Troubles. <SEP> <P3-S0> Ireland and the United Kingdom are both part of the European Union (EU). <P3-S1> In 1997, this area required formal recognition during the course of negotiations for the Amsterdam Treaty of the European Union and is now known as the Common Travel Area. <P3-S2> The Crown Dependencies are not a part of the EU however do participate in certain aspects that were negotiated as a part of the UK's accession to the EU. <P3-S3> Neither the United Kingdom or Ireland are part of the Schengen area, that allow passport-free travel between EU members states. <P3-S4> However, since the partition of Ireland, an informal free-travel area had existed across the region. <SEP> <P4-S0> 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. <P4-S1> most of these were the protestant descendants of colonists from great britain. <P4-S2> however, a significant minority, mostly catholics, were nationalists who wanted a united ireland independent of british rule. <P4-S3> 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.