During the constitutional convention, the commerce and the slave trade compromise gave congress the power to

The Commerce and Slave Trade Compromise was a meeting of states whose representatives were making plans for the National government. There was a dispute between the states in the North and South. A compromise was made by giving the Congress the power to not prohibit the slave trade until 1808, however, imported slaves could be taxed.  

amend the Constitution of the United States with a majority vote

Explanation:

there are hundreds of postives ways to unite a country with another country here are a   few

1 peace treaty's peace treatys

are basically a document signing a allliance with one country and another.

2 gift

what i mean by this is for example how the french gave the americans the statue of libery a gift of peace.