Abstrakt
The world of today is vastly different from the world, in which states laid down roots and basis of the international law system as a normative framework for their coexistence. The trends toward globalism and (necessary) interstate cooperation gave rise to new actors in international politics, among which international organisations are the most important "new" actor.
They serve for States (and sometimes also other actors) as international cooperation fora, which allow sovereign nations to accomplish common goals. Even some of these goals may be accomplished by States individually, most of them require international cooperation.
And among such goals are also issues crucial for the survival of the whole international community: peace, security, human rights, environmental protection, etc. No state - no matter how prosperous or powerfull - can address these issues effectively on its own or through restricted tools such as international conferences.
Global problems require a coordinated and effective response; it is international organizations, which can facilitate such response. Most changes in international law since 1945 have occurred within the framework of international organizations.
Moreover, international organisations as one of the institutionalized forms of cooperation (without which the existence and functioning of international community of today is unthinkable) can be created to fulfill nearly all imaginable goals. This is the reason for their meteoric rise and the reason why most of issues coming in the world news headlines' are or will be adressed by some of the international organisations.