Complex sentence: After a brief stay in Berlin, he arrived in Paris, where he joined the existing Romanian socialist group comprising, among others, Christian Rakovsky, Ioan Sion and Barbu Lăzăreanu.
Split into simpler sentences: After a brief stay in Berlin, he arrived in Paris. There he was integrated in the Romanian socialist group already existing there, which also included Christian Rakovsky, Ioan Sion and Barbu Lăzăreanu.