Beyond the obvious immediate consequences for the future of Israeli politics, Ariel Sharon's decision to leave the Likud and set up his own party may signal a realignment of the country's political map. Until 1967, the Likud and its predecessor parties - Herut, Gahal - were marginal phenomena in Israel's politics. Their intellectual parent movement was Jabotinsky's Revisionists, whose main characteristic was a principled opposition to the idea of partition as envisaged by the 1947 UN decision that paved the way for Jewish statehood. Before and during the founding years of the state, the hegemonic power was the Labor movement allied with the middle-of-the-road liberal General Zionists and the Religious Zionists of Mizrahi. These parties all accepted partition - albeit with a heavy heart, but as the only way of achieving Jewish sovereignty in the Land of Israel. The Revisionists' opposition to partition waned a bit after 1948, yet it always kept them at the margin of the country's real political discourse: Laborites and liberal Zionists could disagree about economic politics, and Mapai and Mapam could quarrel about attitudes to the Soviet Union and social policies: In the years of mass immigration of the 1950s and 1960s these were crucial issues, relevant to the new nation's survival and development. ARGUMENTS ABOUT historical rights to Hebron, Jenin, Jericho or Nablus looked utterly irrelevant to the attempt to establish and consolidate a Jewish nation-state under extremely difficult conditions. Implicitly, even Menachem Begin recognized it, never even once calling, between 1949 and 1967, for a military initiative to gain control of Judea and Samaria, or even the Old City of Jerusalem. All this changed in the Six Day War. Overnight, forgotten and sometimes consciously repressed sites of millennia-old Jewish history returned to the center of the political discourse - and the daily experience of millions of Israelis. It is one thing to claim territories beyond your borders, quite another to insist on keeping what you have come to actually control. None other put it better than Moshe Dayan, the almost archetypical scion of the Labor movement: "We returned to Shiloh and Anathot so as not to relinquish them - forever." In other words: the Likud agenda - that all the Land of Israel west of the Jordan River should remain part of Israel - became a reality, not a far-fetched dream. What appeared, before 1967, to be at best a utopian dream, at worst a chauvinistic call to arms, turned into the quotidian reality to which Israelis from all walks of life and from all political orientations became deeply attached. It took the Likud some years to win an election; this happened only in 1977. The immediate causes were apparent - a discredited Labor Party, seen as responsible for the Yom Kippur War debacle, and the emergence of Yigael Yadin's DMC Party, which took most of its votes from Labor. But on a more fundamental level this signified a paradigm change in Israeli politics: Social and economic issues took a back seat, the nationalist project of an undivided Land of Israel moved to center stage. By setting up the Likud in 1973, Sharon gave this paradigm shift its institutional expression. First the Gaza disengagement, and now Sharon's leaving the Likud, seem to suggest a turnaround: When someone like Sharon realizes that the dream of an undivided Land of Israel is a chimera - and a dangerous one - something fundamental has changed. As public opinion polls suggest, more than half of the Likud's voters seem to follow him, realizing, as he appears to, that Israel has to define its borders on the basis of the acceptance of a two-state solution, i.e. partition. The hard core of the Likud - about 10-15% of the voters - appears to be loyal to the old Revisionist dream of an undivided Land of Israel: This was historically the size of the Likud in pre-1967 days. The parallel shift in Labor to more social-democratically oriented policies under Amir Peretz suggests a similar return to the pre-1967 agenda: away from a nationalist ideology and back to issues of social and economic justice. Just as 1967 was a major watershed it appears that - beyond the personal enmities and ambitions which are obviously part of the scene, Sharon's moves, first disengagement, now leaving the Likud - a new watershed in Israeli politics has been reached. The writer is professor of political science at the Hebrew University of Jerusalem.