What two countries did the act of union unite?

There have been three separate Act of Unions, all used by the United Kingdom.

The first, the Act of Union 1707, united the countries of Scotland and England (forming Great Britain).

The second, the Act of Union 1800, united the countries of Ireland and Great Britain (forming the United Kingdom).

The third, the Act of Union 1840, united the Upper and Lower Canadian legislatures, forming a single Province of Canada within the United Kingdom.