Complex sentence: AAFC owners had already discussed merging with the National Football League (NFL) the previous year--most teams in both leagues were losing money--although the talks fell apart when they could not agree on which of the AAFC's teams would join the NFL.
Split into simpler sentences: AAFC owners had already discussed merging with the National Football League (NFL) the previous year, and most teams in both leagues were losing money. The talks fell apart, however, when the owners could not agree on which of the AAFC's teams would join the NFL.