FROM the bullet-pocked walls of Croatian villages to the wooded shores of the Crimean peninsula, the eastern half of Europe is struggling under the weight of history's unanswered questions.After centuries of war, the empires of western Europe seem to have settled into a more modest definition of their national identities. But in the east, the remains of the Austro-Hungarian Empire were buried under the edifice of the last great empire of Europe, the Russian Empire, albeit in its modern, Soviet form. Unfinished battles over borders and the unfulfilled yearnings of divided peoples were concealed after World War II under the weight of the Red Army and hidden by the rhetoric of Communist inter nationalism. The first crumbling of the Soviet Empire took place in central and eastern Europe, as the vassal states of Poland, Czechoslovakia, Hungary, Bulgaria, and Romania freed themselves from its weakened grasp. Now Czechs and Slovaks have resumed debate over the future of their federation. Hungarians look longingly at their brethren and lost lands across the border in Romania. Poland begins to exert its influence in the lands wrested from it in Lithuania, Byelorussia, and the Ukraine, where many Poles still liv e and their churches still stand. Here on the western frontier of the Soviet Empire, the talk is of independence, of the restoration of a Ukrainian nationhood only dimly remembered and highly embellished in Ukrainians' eyes. Barely had the doors of the Communist Party Central Committee been shut in Moscow and the slogans of proletarian internationalism stilled when Ukrainians and their Russian brothers set to resume their own unfinished historical battles. Within days of the Ukrainian declaration of independence Aug. 24, the Russian republican government of Boris Yeltsin issued a statement to the effect that the present borders were valid only so long as the Ukraine remained in the Soviet Union. Should it leave, a Yeltsin spokesman suggested, the fate of Russian-populated areas of the Ukraine, including the east and the Crimean peninsula, is up for grabs. And as he was quick to remind, in the boundaries of the national republics of the Soviet Union formed after the Bolshevik revolution, the Crimea was made part of the Russian Federation. In 1954, shortly after Joseph Stalin's death, Nikita Khrushchev gave the Crimea to the Ukraine to mark the 300th anniversary of the unification of the Ukraine and Russia. "I don't see why a gift like that should be permanent in a situation of secession," one of Moscow's new leaders, Arkady Volsky pronounced. Here in Kiev such talk sparks its own response. Outside the headquarters of Rukh, the nationalist, democratic political movement, a political cartoon shows Yeltsin, a Napoleonic cap perched on his head, pointing across the border of the Ukraine and proclaiming that wherever "our people are, is ours." But Mr. Volsky launched into a vigorous defense of the Russian statement. After all, "Crimea was won by Russian warriors in wars with Tatar Khans," he said defiantly. "It is Russian territory originally." Rukh leader Vyacheslav Chernovil rejects Volsky's claims. Crimea was the land of Tatars, protected by Turkey until the end of the 18th century. "Crimea was captured not by Russia, but by the Russian Empire, and the Ukraine was a part of this [empire]," he asserted. "Economically and historically, Crimea is bound with the Ukraine." His argument shows that the work of scholars in dusty historical archives is now the stuff of many political wars to come.