Complex sentence: Lunacharsky became a Marxist at the age of fifteen, and after studying at Zurich University where he met figures such as Rosa Luxemburg and Leo Jogiches he joined the Russian Social Democratic Labour Party.
Split into simpler sentences: Lunacharsky became a Marxist at the age of fifteen. While in Zurich, he met European socialists like Rosa Luxemburg and Leo Jogiches and joined the Russian Social Democratic Labour Party.