I think releasing their movies in smaller markets generates an amazing amount of hype in readiness for the two biggest markets - domestic US and China.
Based on the amazing critic and audience reviews, as well as the numbers already generated internationally, I think it's safe to say Civil War will make $550m in the US (in fact I think that's slightly conservative).
Add in $150m from China and $30m from Russia then yeah I can easily see CW reach the $1b mark with additional international revenue.
The other big thing it has in it's favour is Spiderman. I think word of mouth is going to spread over his role and just how good the character is in this movie (no spoilers) and that character alone is probably worth about $100m all told for this movie.