Complex sentence: FC Annecy, formed in 1927, spent the majority of their history in regional amateur football--the club turned professional in 1942 but were compelled to return to amateurism a year later.
Split into simpler sentences: FC Annecy, formed in 1927, spent the majority of their history in regional amateur football. The club turned professional in 1942, but was compelled to return to amateurism a year later.