Complex sentence: However, he was most interested in promoting stamp collecting and in the creation of stamp clubs, and he attended most of the American Philatelic Society stamp shows and conventions held during his lifetime and created philatelic souvenirs for them.
Split into simpler sentences: However, he was most interested in promoting stamp collecting and in the creation of stamp club. He attended most of the American Philatelic Society stamp shows and conventions held during his lifetime and created philatelic souvenirs for them.