England and Scotland united under the same king (James I / VI) in 1603, and became fully unified as Great Britain in 1707. So historically the oppression in Ireland, India etc as well as the colonial history was done by the joint crown and administration of England and Scotland

That said, it's not quite so simple. There's a pre-unification history of invasion and war, there's power struggles between kingdoms early in the 17th century, and up to and in modern times arguments around being controlled, exploited and neglected by a majority English government.