Every time when Russia and America got in a fight during the world meeting that was too destructive. So other countries, after they saparated then again, made them promise that they will never touch each other. Thet was meant that they wouldn't fight, but, either America and Russia took their promises too serious, or even that was unfotunately worded magical vow, but they ended up avoiding absolutely any physical contact. Like, you know, no hand shake, no pat on the shoulder and so on. Even after both of them acknowledged that they maybe kinda like each other.
Not just like, in fact, but longing, USTing and starving.

The rest is up to you, author. I hope for happy end and smut :3