BERLIN — Chancellor Angela Merkel of Germany recoils from the idea that she is now, almost de facto, the leader of the Western world, the defender of trans-Atlantic alliances and multilateralism. But like it or not, she and the country she will lead for a fourth term have become global actors.

Germany may be a “reluctant hegemon,” but it is a hegemon nonetheless, the largest, richest and most important country in Europe, itself the richest region on the globe. It is often said that Germany is too big for Europe and too small for the world.

But with the presidency of Donald J. Trump and the newly aggressive and authoritarian leaders of Russia, Turkey, Hungary and Poland — and now a rearing of the far-right in Germany’s election on Sunday — Ms. Merkel has had leadership thrust upon her.