Geographically, the British Isles are the two main islands of Great Britain and Ireland and all of their off-shore islands. Politically, they are comprised of the United Kingdom and the Republic of Ireland.
There are many river islands in the British Isles but no two comprise them
The United Kingdom has the largest population of the two British Isles nations. (UK & Ireland)
Great Britain and Ireland make up the British Isles
Great Britain: comprising England, Scotland and Wales, and Ireland: comprising Northern Ireland and Eire.
Ireland and Great Britain (the United Kingdom).
Geographically, the British Isles are the island of Great Britain and the island of Ireland. Politically, they are comprised of the United Kingdom of Great Britain and Northern Ireland and the Republic of Ireland.
There are only 3 nations which comprise Great Britain - England, Scotland and Wales. The 4 nations which comprise the United Kingdom of Great Britain and Northern Ireland (or UK for short) are England, Scotland, Wales and Northern Ireland. To further confuse matters, the British Isles comprise the island of Great Britain as well as the island of Ireland even though not all of Ireland is part of the UK - and also around 6,000 smaller islands that surround the two main islands.
British isles
Because they both rely (and relied) on ships for trade and commerce.
No, there is no single leader of the British Isles. What is called the British Isles has a number of countries and they each have their own leaders. The British Isles is a geographical reference, not a political one.
The British Isles are not a group of cities, but rather a group of relatively large, heavily populated and industrialised islands/nations. There are hundreds of cities on the British Isles. The British Isles are a group two main islands - Great Britain and Irealand, plus hundreds of smaller islands, such as the Isle of Man and the Orkneys. A $5 atlas or a search on the web or even in wikipedia will garner the answers you seek...
Great Britain and Ireland are the two main islands but there are also hundreds more small off-shore islands.