Can a country that is divided still be successful?

Yes, but not to its potential.

Explanation:

America may be one country but the country is divided in politics. That is why we have roughly half of the senators are republicans and half are democrats. Bills still get passed, but not as fast as we want them to be passed.

If everyone thought the same way, a country will be running at very successful level. However, that is dreaming.

Mostly every country is divided in some way: age, politics, war, etc.

TL; DR: Yes, but you cant reach the highest potential