BERLIN — With the results of Spain’s election on Sunday, a tumultuous 2015 for Europe is ending on a stinging note that underscores Germany’s increasing isolation and Europe’s deepening division.

Spain’s voters followed those in Portugal and Greece this year in punishing a conservative government that had allied with Brussels, Berlin and international creditors in carrying out the austerity policies pushed as the solution to Europe’s debt crisis.

In 2016, that trio of powers will have fewer friends to turn to. Successive elections have helped to hollow out the political center in Europe, raising the question of what will keep the 19 countries that use the euro and the nine other members of the European Union that do not marching forward together.

After the Spanish vote, Italy’s prime minister, Matteo Renzi, a center-leftist who had built a good relationship with Chancellor Angela Merkel of Germany, renewed his attack on austerity and, quite nearly, Ms. Merkel personally, effectively blaming her policies for the rise of populism across Europe.