What were the two competing alliances in Europe?

Answer 1

It depends on what time period you're referring to, as there have been at least four instances where Europe was divided in two alliances:

Thirty Years' War;

Europe, mainly Western Europe, was split into two sides: Protestants and Catholics.

World War I;

Europe was split into two major alliances: the Allies and the Central Powers.

World War II;

Europe was split into two major alliances: the Allies and the Axes.

Cold War;

Europe was split into two opposing sides: democratic Western Europe and communist Eastern Europe.