I agree with the previous posts that alliances are a necessity in this world. Alliances have existed for a very long time and have assisted countries tremendously in the pursuit of the goals of that nation. The oldest alliance in the world is the Anglo-Portugese Alliance. It was signed in 1373 and involves England and Portugal.

During times of war for example, it is very important to have military allies. Other nations may have resources that are not available. Numbers are also important here because a country may be up against another country that doubles their numbers in military personnel.  

I would also have to argue that alliances are more important today than ever before. We are becoming an increasingly global society both in terms of international policy and in terms of business and the economy. We are also starting to realize that what one country does to its environment impacts us on a global level. From international legislation relating to human rights (universal declaration of human rights) to international attention to environmental policy (Kyoto Protocol) we are becoming a much larger, much more unified country. At the same time, there are still threats, countries that have their own desires that are in opposition to a global society. These countries are becoming more and more powerful, posing a greater threat than ever before. As a result, we need alliances to keep us safe, to help us establish unifying policies that work on a global level, and to encourage open lines of communication that will maintain peace and discourage perpetuation of violence and terrorism.

I would suggest that alliances are more necessary now than ever before.  I think that as we progress into a new era of geopolitics where threats and enemies might be present in areas unknown to us, the need to forge alliances, share intelligence, and broaden the reaches of diplomatic horizons is more needed now more than ever.  I am not sure it is wise to presume that some area of the world that is deemed as "remote" and "unimportant."  In an increasingly globalized world, it is essential that alliances are forged and nations seek to make our widened world a more "flat" one and one that shares and understands one another as opposed to demonizing them.

I do not think that alliances are necessary in the same way that they used to be, but I think they are still useful.

In the old days, alliances were like a life or death thing.  Countries made alliances to keep from being destroyed.  For the US, at least, this is no longer a serious worry.

But alliances are very helpful because they can make it easier to get countries on your side when you try to do something diplomatic.  For example, it is hard for the US to get tough sanctions on Iran or North Korea because we are not allies with the Russians or Chinese and they tend to block our efforts to sanction those countries.

I would say most definitely. Many of the threats countries face in the world in the modern age are problems faced by entire continents, regions, or the globe.  Alliances, military or economic, help these countries to provide a united front to deal with these issues.

NATO and the UN serve as deterrents to some aggression by individual nations, and they have cooperated to end the Yugoslav Civil War, provide peacekeepers in conflict zones all over the globe, and cooperate on issues from terrorism to AIDS to Climate Change.

These organizations and alliances, therefore, prevent aggression and solve world issues.