The Brezhnev Doctrine asserted that the Soviet Union would start becoming an important and interfering force in the Eastern part of Europe for one reason only - to preserve communist rule. A part this doctrine was also that they would want to obtain a disarmament agreement between themselves and NATO.
This doctrine asserted to give limited independence to the satellite states under the Soviet Union. The doctrine justified the invasion in Hungary as well. This doctrine urged to maintain socialism that is slowly diminishing in some satellite states. The makers of the doctrine believe that these satellite states are slowly shifting from socialism to capitalism
