The Balkans.
Europe and Asia
Russia is half in Europe and half in Asia.
It is Both Europe and Asia
the steppes
Austria Italy France Poland Russia
Poland
Germany was the strongest European country in Europe in 1914.
The highest mountain in Europe is Mount Elbrus located in Russia (Caucus region)
The Big Four of Europe, United Kingdom, Austria, Prussia and Russia.
The Ukraine (Eastern Europe, close to Russia)
Serbian nationalism increased tensions within Europe before World War I. Serbia wanted to create a pan-Slavic state in the Balkans which included Bosnia-Herzegovina, held by Austria-Hungary. Serbia was allied with Russia and Austria was allied with Germany. Russia allied with France. A war between Serbia and Austria threatened to involve the whole of Europe.
Arguably Russia or Austria-Hungary. This is as simple as I can say it.