Truce clarification (ethical question)

I have a question about a truce that was set up between myself (green) and pink in game 2490397. The truce was set up between Benin and Nigeria and while it has outlived it's usefullness, it is still in effect. My understanding is that it is only that border that is affected. Now that only pink and I are left, I have an opportunity with my cards to do some serious damage and maybe take him out. I assume that it is ethical to conquer Nigeria from the other side and I will take out Nigeria as the last one. Is this OK?