Complex sentence: Following the expulsion in February 1925 the opposition began to publish a journal, "Gegen den Strom", and, at a congress held on December 30,1928, they officially became the KPO.
Split into simpler sentences: Following the expulsion in February 1925 the opposition began to publish a journal, "Gegen den Strom". And at a congress held on December 30,1928 they officially became the KPO.