To begin with, one of the aims of the congress was to bring peace to Europe. This meant that power had to be evenly distributed, balanced in other words. As a result, it was agreed that the five European powers (Russia, Austria, Prussia, France and United Kingdom) had to have an even share in the influence they have and the land they possessed too. As the other powers feared the return of a strong France, the country was forced to return to its old borders (the 1790 borders). In this congress the first signs of collective security came into play. To further strengthen chances of peace in Europe, it was agreed that the countries were free to do whatever they wanted. However should this sort of independence turn encourage a particular power to threaten another power, then all other powers were allowed to take action against that particular power (refer to page 59 of History of Europe and the Middle East Course Companion).
The reason for this idea of collective security was because it would help keep the balance between powers in terms of influence and land. Also, the countries at the congress learnt from their mistakes. Their main mistake was allowing Napoleon to invade other European countries and as a result, he became so powerful that the other powers could do nothing to stop him.
Furthermore, to make it harder for France to attack or threaten the other European powers, smaller countries in Europe were increased in size. Not only was this done, new states were created to. These new or enlarged states were known as buffer states. The main advantage of these buffer states was that in order for France to attack the other European powers, she would have to go through these buffer states. This on the other hand