Complex sentence: In several countries, stereotypers and electrotypers joined together to form labor unions around 1900 that persisted into the 1970s; in the US, the union had 10,500 members in the 1950s.
Split into simpler sentences: In several countries, stereotypers and electrotypers joined together around 1900 to form labor unions. These unions persisted into the 1970s; in the US, the union had 10,500 members in the 1950s.