USA threat to the world economy or to stabilize the world?

Usa is a great country. It is the biggest Economy and therfore automatically is the prefect of the rest of us Whenever a country is bullied by another like in case of Iraq and Kuwait. They intervene. it is impossible to stay without a leader. In any case if it is not America there would be another country. America has to work hard to remaib Number one otherwise other Nations may emerge and wrestle it from this coveted position.Especially China