Constituent country

A constituent country is a type of country which serves as an administrative division. Constituent countries usually form together to make a larger sovereign country (such as the United Kingdom, a sovereign territory made up of four countries). Unlike federal countries, power between constituent countries may not be spread out evenly, with one of them usually holding the capital and government.
United Kingdom
The United Kingdom is a sovereign country made of four constituent countries. They are (in order of size) England, Scotland, Wales, and Northern Ireland. While all four are often referred to as countries, they are technically constituent countries within a sovereign country; UK. They are also sometimes referred to as regions, provinces, nations, or statelets. However, these titles are problematic and in particular, sensitive in Northern Ireland.
Even though Scotland, Wales and Northern Ireland have been given their own devolved assemblies, the UK Government still deals with most nation-wide matters and directly administers England.
England is the largest and most populous country of the United Kingdom. Unlike the other three, it does not have its own government and is directly administered by the UK Parliament, which is mostly made up of English politicians. The capital of England (London) also serves as the UK capital. The King of the UK also primarily lives in England. England united with Wales in 1277. It later united with Scotland in 1707 and Ireland in 1803.
Scotland is the second largest and second most populous of the four UK countries. It has representation in the UK Parliament as well as having its own legislature, located in Edinburgh. Scotland arguably has the most autonomy out of the four countries. As well as being part of the UK, Scotland has its own distinct culture and language. Scotland and England united in 1707.
Wales is the third largest country by population and size and it borders England. The Welsh Parliament is the devolved assembly which governs Wales. The capital is Cardiff. Like Scotland, Wales has kept its distinct culture and language as part of its institutions.
Northern Ireland is the smallest country by area and population. It has been described by different sources as a country, region or province. The capital is Belfast and the legislature is the Northern Ireland Assembly.
Kingdom of the Netherlands
The Kingdom of the Netherlands is made of 4 constituent countries. They are the Netherlands proper, Aruba, Curacao and Sint Maarten all in the Caribbean. The countries of the Kingdom all have high degrees of autonomy, with the European Netherlands only retaining power for defence and international relations. Everyone born in the Kingdom has Dutch nationality.
Earlier (before 10 October 2010) it had 3 constituent countries: the Netherlands proper, Aruba and the Netherlands Antilles. Before 1975 Suriname was part of the Kingdom of the Netherlands.
The Netherlands is the largest country in the Kingdom by size and population. It shares its name with the Kingdom of the Netherlands due to being the oldest part. The capital is Amsterdam but most government buildings are in the Hague.
Curacao is the second largest by population. It is an island in the Caribbean. The capital is Willemstad. The official languages are English, Dutch and Papiamento.
Aruba is the third largest by population. It is also a Caribbean island. The capital is Oranjestad.
Sint Maarten is the smallest by population and size. It is located on half of the Caribbean island Saint Martin, the other half being a territory of France. This means that Sint Maarten's border with France is the only Dutch-French border. The capital is Philipsburg.
Kingdom of Denmark
The Kingdom of Denmark is a sovereign state in Scandinavia, located in Europe. Denmark is made up of three constituent countries: Denmark, Greenland, and the Faroe Islands. Similar to the Kingdom of the Netherlands, the countries of the Danish Kingdom are highly autonomous. Denmark retains powers for international representation and defence.
Denmark is the largest country by population out of the Kingdom's three countries. It shares its name with the Kingdom due to being the sole original part of it. The capital, Copenhagen is located here and directly administers Denmark.
Greenland is the largest of the three countries by size. The capital is Nuuk. It is located in the North American continent.
The Faroe Islands is the smallest by area. The capital is Torshavn.
China
In China there are two special administrative regions which are sometimes referred to as countries.
Other relationships
Countries may be held (usually by force) as part of a larger country or federation of countries. An example of this was the Soviet Union, which held various countries in eastern Europe by force for up to 70 years.
Many dependent territories exist. They tend to be small countries or islands which larger countries have "collected" in the course of their history. For example, Niue is considered to be a country even though its sovereignty belongs to New Zealand.
The Channel Islands are not part of the United Kingdom, but are "Crown Dependencies". Sometimes people refer to the Crown Dependencies as countries.