Croatia, officially the Republic of Croatia, is a country at the crossroads of Central and Southeast Europe on the Adriatic Sea. It borders Slovenia to the northwest, Hungary to the northeast, Serbia to the east, and Bosnia and Herzegovina and Montenegro to the southeast, and it shares a maritime border with Italy. Its capital and largest city, Zagreb, forms one of the country's primary subdivisions, along with twenty counties. Croatia has an area of 56,594 square kilometres (21,851 square miles) and a population of 4.07 million.

The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK or U.K.) or Britain, is a sovereign country located off the north­western coast of the European mainland. The United Kingdom includes the island of Great Britain, the north­eastern part of the island of Ireland, and many smaller islands. Northern Ireland shares a land border with the Republic of Ireland. The total area of the United Kingdom is 94,000 square miles (240,000 km2).