power to make treaties with other countries..

The executive branch of the government has the power to make treaties, but each treaty must be ratified by the US Senate

The plural of the word "treaty" is "treaties."

It is up to the country not a state to make treaties. It wouldn't make sense for a state to make a treaty with a foreign government because a treaty applies to an entire country and not a particular state.

The Executive Branch makes the Treaty, this branch includes the President, the US Senate ratifies the Treaty by a two thirds majority. Only then is it effective.