HAVANA—Raul Castro confirmed he was handing over the leadership of the Cuban Communist Party to a younger generation at its congress that kicked off on Friday, ending six decades of rule by himself and older brother Fidel. In a speech opening the four-day event, Castro, 89, said the new leadership were party loyalists with decades of experience working their way up the ranks and were “full of passion and anti-imperialist spirit.” Castro had said at the last party congress in 2016 it would be the last one led by the “historic generation” who fought in the Sierra Maestra to topple a U.S.-backed dictator in the 1959 leftist revolution. He already handed over the presidency to protege Miguel Diaz-Canel, 60, in 2018. The congress is the party’s most important meeting, held every five years to review policy and fix leadership. “I believe fervently in the strength and exemplary nature and comprehension …