The struggle between the workers' parties and the right-wing Revisionists took an increasingly central place in Zionist history beginning in the 1930s. The Labor Movement gained political hegemony during the period of the Yishuv (pre-state Israel). When Jabotinsky tried to challenge Mapai's power position he suffered a bitter defeat. Most of Israel's first 13 years were marked by political polarity between Mapai and the Herut Movement (the latter led by Begin). Herut received a thrashing in the Knesset elections in 1951 and the General Zionists (GZ) became the second largest party after riding on the wave of middle class protest against the Mapai led government austerity regime. However, it failed to exploit its broad support into a permanent electoral base that would transform the right-center bourgeoisie into a political force that would serve as an alternative to Ben-Gurion's government. In the summer of 1955, Herut replaced the GZ as the second largest Knesset party, and in 1959, Begin became head of the opposition after Herut won 17 seats, twice as many votes garnered by the GZ, which was reduced to its political size of the first Knesset elections in 1949. The key political rivalry returned to the power struggle between the Zionist left and the nationalist right.