halacha - Ose shalom post shemona esre

Basic Background:

Following the shemona esre prayer, the sages instituted concluding the prayer with the verse "yihyu leratzon" followed by "petira"- symbolically exiting from before G-d through taking 3 steps backward. There are other customs as well, such as additional supplications prior to "petira" and prayer for the rebuilding of the temple following "petira".

Directly following the "petira" we say a prayer "ose shalom bimromav", that G-d should grant us peace. While saying this prayer, it is customary to bow to either side and forward. My questions are:

Questions:

1. Why is this prayer here? It seems to end other prayers as well such as kaddish and the harachamans following bentching. Is there a common thread?


2. Why would we need to pray for peace here if we just ended the shemona esre with a blessing for peace?

Any history behind the institution of this prayer in general would be helpful as well.