Complex sentence: In 1956, the IRFU and WIFU formed a new umbrella organization, the Canadian Football Council (CFC), and in 1958, the CFC left the CRU, becoming the Canadian Football League.
Split into simpler sentences: In 1956, the IRFU and WIFU formed a new umbrella organization, the Canadian Football Council (CFC). In 1958, the CFC left the CRU and became the Canadian Football League.