Simplify the following text for a Grade 10 native English-speaking person.
Original: It was formed by the merger of the Kingdom of Great Britain ( itself having been a merger of the Kingdoms of England and Scotland ) and the Kingdom of Ireland , with Ireland being governed directly from Westminster through its Dublin Castle administration .
Simplified: It was formed by the merger of the Kingdom of Great Britain ( itself having been a merger of the Kingdoms of England and Scotland ) and the Kingdom of Ireland .