Complex sentence: The party was founded in Bucharest on July 15,1928, as a leftist splinter group of the Social Democratic Party, formed by a minority that opposed the cooperation with the National Peasant Party.
Split into simpler sentences: The party was founded in Bucharest on July 15,1928. The PSMR was the product of a split in the Social Democratic Party, formed by a minority that opposed the cooperation with the National Peasant Party.