Complex sentence: Political union between England and Scotland was established in 1707 with the creation of the Kingdom of Great Britain and thereafter, in 1801, the Kingdom of Ireland merged with the Kingdom of Great Britain to form the United Kingdom of Great Britain and Ireland.
Split into simpler sentences: Political union between England and Scotland was established in 1707 with the creation of the Kingdom of Great Britain. In 1801 the Kingdom of Ireland merged with the Kingdom of Great Britain to form the United Kingdom of Great Britain and Ireland.