" Maastricht had three significant side-effects. One of them was the unforeseen boost it gave to NATO. Under the restrictive terms of the Treaty it was clear (as the French at least had intended) that the newly liberated countries of eastern Europe could not possibly join the European Union in the immediate future—neither their fragile legal and financial institutions nor their convalescent economies were remotely capable of operating under the strict fiscal and other regulations the Union’s members had now imposed upon all present and future signatories.
Instead, it was suggested in the corridors of Brussels that Poland, Hungary and their neighbours might be offered early membership of NATO as a sort of compensation: an interim prize. The symbolic value of extending NATO in this way was obviously considerable, which is why it was immediately welcomed in the new candidate member-states. The practical benefits were less obvious (unlike the damage to relations with Moscow which was real and immediate). But because Washington had reasons of its own for favouring the expansion of the North Atlantic Defense community, a first group of central European nations was duly admitted to NATO a few years later. "
― Tony Judt , Postwar: A History of Europe Since 1945