for now, the unification is impossilbe. A war across the straignt is more likely than the unification. US has done a lot of things on cross-straight issue. US is not willing to see that a peace between mainland and taiwan. The present tense situation is what they wanna see. They can benefit from it, for instance selling weapons to taiwan. The mainstream of Taiwan's politics is democracy which China mainland doesn't have. At present, it's hard to merge taiwan's democracy process to mainland china.