The United States was born in an imperial world, and grew to economic preeminence in an era of intense globalization. At first its citizens experienced empire as the struggle with the motherland and among the contending European powers that fought over North America and in the North Atlantic from 1750 to 1815. From 1815, this inter-imperial entanglement became increasingly focused on the relationship with the British empire. The American empire as both aspiration and practice emerged from and was heavily influenced by this relationship. Having developed its own imperial agenda under the hegemony of British naval and economic power on a global level, the United States gradually came to challenge this unequal relationship. Informal and formal empire are relevant to such trans-imperial entanglements as are non-state actors such as missionaries and entrepreneurs.