An alien has just landed from outer space. Explain to that alien the purpose of government.

I believe that I'd use the current definition of government or the political direction and control exercised over the actions of the members, citizens, or inhabitants of communities, societies, and states.

The purpose of our Federal Government, as found in the Preamble of the Constitution, is toestablish Justice, insure domestic Tranquility, provide for the common defense, promote the general Welfare, and secure the Blessings of Liberty to ourselves and our posterity.