Original: Zhvanetsky's and Kartsev's success in 1970s, together with Odessa's KVN team, much contributed to Odessa's established status of a "capital of Soviet humour", culminating in the annual Humorina festival, carried out on and around the April Fool's Day.
Simplified: Their success in 1970s contributed to Odessa's established status of a "capital of Soviet humour".