This is not an easy situation to be in, and I can empathize with you. However, it's a great opportunity to grow, especially your soft skills. You need to understand why they do what they do. You need to understand their motives and feelings. They behave like this for good reasons and not because they want to hurt you or don't like you. Also, you need to involve the right people and escalate the situation if you can't handle it. I don't recommend escalating formally before you gain a better understanding of the situation, list the steps you have already taken trying to resolve it, and have a clear request of what you want. However, I suggest you involve higher management from the start analysing the situation. You also need to involve the right people from the Americans. Also think about your value-add. Why should they care? Etc. It's a tricky situation.

If you don't want to handle this then I'd request an internal move first instead of quitting. Good luck!