Does balance of power still matter in international politics?
Most definitely, balance of power is a factor in international politics. However, while in the past, that balance of power was about military force and weaponry, the focus has switched to a large degree to economic power and control over natural resources. For example, during the Cold War, with the Soviet Union, the emphasis was on who had nuclear capability and all attempts to keep the peace involved either an arms race or negotiation to assure that one's enemies did not have more nuclear capability. It is true that the present discussion and negotiation over Iran's nuclear capabilities still have that focus, and most of the world continues to condemn North Korea's testing of its nuclear weaponry and delivery systems. But economic power has become increasingly important, as has the power to own or at least use the natural resources so unevenly distributed around the world.
The power of one's economy, one's standing in the economies of the world, is the kind of power we concern ourselves with today. There was a time when the western world held all of the economic power quite firmly in its reins. Today, though, developing nations such as India and China are becoming economic world powers as well. A country that is a trading partner, one who buys and sells goods to another country, can easily cause economic damage to a country, for example, by refusing to sell goods or refusing to buy goods. Since no country produces everything the country needs, it is easy to see that one country could cripple another. And trade imbalances are not good for an economy, buying more than one is selling to another country, so this is another kind of balance of power that is important.
Since the natural resources of the world are so unevenly distributed, who controls them is a vital factor now in the balance of global power. Some countries have platinum; others have oil. Some have climates in which they can grow crops that other countries cannot. Who controls what resources is part of the balance of power today, everything from disputes over rights to the Arctic to who is going to control any natural resources on other planets. Control over these resources is so important, this is considered an aspect of national security. A country that cannot fuel itself effectively is a nation at risk.
Now, having said all of that, I also need to point out that in today's world, the traditional notions of a balance of power amongst nations are rapidly eroding because of border-transcending radical terrorism. ISIS and other such groups operate unconventionally, with no acknowledgement of the borders agreed upon by the world's nations, gaining power here and there, in numerous nations, agreeing on some goals and strategies, but fragmented in some ways, too. How can one assess the balance of global power under such circumstances? It is not even clear what constitutes power in such a context. Is it raw numbers, territory held, the sheer brutality of these groups creating a power? This is a complicated issue, and the nations of the world, which have focused on military, economic, and resource power, seem ill-equipped to maintain their power over these groups.