Some Nato advocates argue that peace would have ruled the Caucasus had the western alliance offered Georgia a membership action plan last spring. Actually, Georgian and Russian perceptions of potential Nato support for Georgia probably radicalised both sides, making war all but certain. In practice, alliances can be destabilising as well as stabilising.
When the cold war ended, many people expected America to rethink its security commitments. Without the Soviet Union and the Warsaw Pact, there seemed little need for Nato. Instead of dismantling or even shrinking its cold war alliances, the US expanded them. Former Warsaw Pact and even Soviet republics were inducted into the 'North Atlantic' Treaty Organisation. The rationale was stability through deterrence: Russia wouldn't dare attack them.
Oddly, proponents of this strategy do not take it to its logical conclusion. If the argument is right, then America should offer a security guarantee to any country anywhere threatened by another. The result would be an era of world peace.
Unfortunately, alliances can promote war as well as peace.
Expanding Nato up to Russia's borders risks a similar impact. The original Nato had a clear purpose: to protect Western Europe from Soviet attack. With the collapse of the Soviet Union and Warsaw Pact, that threat disappeared.
Unfortunately, expanding Nato has made the world more, rather than less, dangerous - at least for the US. The former eastern Europeans possess sub-par militaries which do nothing to help defend America and which actually cost the US money to train and equip. Manpower contributions to Afghanistan and Iraq were more symbolic than real.