LOOKED at in the context of the post-World War II era, the developments Dec. 9-10 in the Dutch city of Maastricht may not seem extraordinary. The heads of the 12 members of the European Community approved treaties that will draw more tightly the threads of unity which have been progressively woven through Europe for 40 years. Of themselves, the treaties may not be historically more important than such preceding steps toward unity as the establishment of the European Community itself in 1957.Viewed against the three centuries of modern European history, however, the Maastricht summit stands out as a salient event. During that period, on no patch of the globe has war been waged more frequently and with greater violence than in Western Europe. Further war among its nations is unthinkable after Maastricht. The solidifying of European unity is being analyzed principally in economic terms. To be sure, the creation of a single European market comprising 350 million people on Jan. 1, 1993, and the issuance of a single European currency before the end of the century will have huge implications both for the prosperity of the community and for international trade and finance. Yet the focus on economics shows how far Europe has come since 1945, when it was buried in the rubble of its second great war in 30 years. The current generation of Europeans is the first since the 17th century for whom the predominant foreign-policy issue has not been regional war or peace. That's the true significance of European unity - not only for Europeans, but also for a world that repeatedly was pulled into European conflagrations. Many loose ends remain after Maastricht. Britain, which still treats European unity as a conspiracy to reverse the outcome of the Napoleonic wars, will continue to agonize over a purported loss of "sovereignty" from European integration. Britain's insistence at Maastricht on a right to pick and choose from the menu of unity's benefits looked haughty and fastidious. As a practical matter, Britain can hardly afford to be isolated from a resurgent Europe, as it will acknowledge in time with loss of face. More important is the role of reunited Germany in Europe. Constructive integration of Germany - the region's most powerful and, historically, most aggressive state - into the affairs of its neighbors has been the foremost motivating factor behind European unity. But Germany is likely to throw its weight around in the family in still unforeseeable ways. Maastricht was a large step forward, but European unification is far from complete.