the acts of union were a pair of parliamentary acts passed in 1706 and 1707 by, respectively, the parliament of england and the parliament of scotland, to make effective the treaty of union which had been negotiated between the two countries. the acts joined the kingdom of england and the kingdom of scotland which had been separate states before, with separate legislatures but with the same monarch into a single united kingdom of great britain. at that time the union flag became the national flag.