ברכת הקב"ה היא שלום, שנאמר ה' יברך את עמו בשלוםThe last berakha of the 'amida, sim shalom, is the blessing in which we ask HaShem for Shalom/peace.
"Grant us peace, goodness, and blessing,
life, grace, kindness and mercy,
for us and on all Israel Your people.
And bless us, our Father, all of us, as one,
with the light of Your Presence..."
Shalom is the highest aspiration of the Jewish people. We do not pray for world dominion or for the death of our enemies. Our ultimate dream is to live in peace with other nations and among ourselves. From the beginning of our history the Tora's utmost promise is that, if we will keep HaShem's commandments we will be left alone by our enemies and live in our land, Israel, in peace and tranquility (Lev. 22:5). In May 14th, 1948, when the modern State of Israel was established, David Ben Gurion read in the Declaration of Independence "WE EXTEND our hand of peace and unity to all the neighboring states and their peoples, and invite them to establish bonds of cooperation and mutual help with the sovereign Jewish people settled in its own land." In our days, this Shalom/Peace is still an ideal (utopian?) aspiration. As if "Peace" could not be considered as the "normal" situation of the Jews but a God given blessing. To certain extent, "Peace" is a miracle, for which we Jews still pray everyday, three times a day.
The text of this berakha is modeled after the most important blessing to be found in the Torah: birkat kohanim. Thus, in birkat Kohainim, we ask for God's blessing (יברכך), then for HaShem to enlighten us with His Presence (יאר ה' פניו) and we end by asking HaShem to grant us the blessing of peace (וישם לך שלום). In sim Shalom we first ask HaShem to bestow upon us all His blessings (peace, life, kindness, goodness, etc.), then we ask Him to bless us with the light of His presence (וברכנו אבינו...באור פניך) , and we end by requesting HaShem to bless us with strength and peace (עוז ושלום).
The Sephardic custom is to say the same text for this berakha in every 'amida, while the Ashkenazi custom is to say this berakha in its entirety only when Birkat Kohanim could be recited, namely, in Shaharit and Musaf. This is why the Ashkenazi custom is to replace sim shalom for shalom rab, a shorter version, for Minha and Arbit.