NATO as one of the regional organizations was created (1949) to provide security against external threats and actor for its memberstates. But this actually meant: Nato's main aim was the deter agression ( which was Soviet Agression for them) in Europe. Another aim was: manage relations among its members. In other words, it aimed to manage intra-alliance relations.
"US in, Russia out, German down" was its motto that explains its main aims shortly...
After Cold War, NATO faced many challenges especially and importantly, NATO faced with existencial problems. Many scholars argues that NATO's business end, Cold War end, no more threat, no need for such alliance type organization anymore...
To survive NAto entered an adaptation period starting from 1991.. NATO's response was quick!
First of all NATO defined some stradegy as response:
1) Establishing Relations with FORMER enemies
2) Defining new security threats
3) Having Relations with EU, dealing with European Security
And actions followed...
@ 1991 Rome Summit: This summit was important to define new strategies to emphasize dialogue with former former enemies.
Just after that summer new institutional response come with NACC ( North Atlantic Cooperation Council) this became a forum for all to sit and talk about everything. Partners were NATO members + Russia + Eastern and Centreal Europe. This was especially for multilateral relations.
@ 1994 PfP Partnership For Peace: This constitute a general framwork for bilateral relations. Resulted with new ideas like: Transformation struxture of military, trainings, peace keeping activities...
with 1992 enlargement process started: for first step: Hungary, Poland, Czech Republic became member and then Estonia, Bulgaria, Litvania, Romania, Latvia, Slovakia became member.
@ 1997 Russia - NATO Council made as framework to regulate relatiıonship. To manage cooperation especially about peace keeping activities and security relationship. This Council meets regularly.
@ 1997 NACC + PFP came together and created Euro-Atlantic Partnership Council established. This was again a multilateral forum fır sonsultation cooperation
In addition to all these:
Nato answered to security challanges by:
~expanding the meaning of security: including human trafficking, terrorism, migration, environmental issues ( proved by making a summit Riga and taking the energy as agenda topic...)
~redefining the military structures : more felxible, mobile structure, more cost effective
~answering the out of area question...