"Le’mishpechotam le’beit avotam-according to their families, to their fathers’ households" is repeated many times in Parshat Nassa. The Mikdash Mordechai says it is by design that this portion contains the laws of Sotah, a woman whose actions destroy the family. The message is that the Jewish People are no stronger than their families. A situation like that of the Sotah can bring down the national family.
The Sifri presents an argument between Rabi Chanina Sgan HaKohanim and Rabi Nossan regarding which peace is the objective of Birchat Kohanim. One opinion is that shalom bayit - peace in the home is what is referred to. The other opinion is that the peace spoken of is political peace of malchut beit Dovid.
The Mikdash Mordechai reconciles these views. National peace can only be achieved if we have peace in our families. It is this dual bracha the kohanim wish to bestow upon us. This is the connection that places Sotah and Birchat Kohanim in the same portion.
Allen Wheelis, a psychotherapist wrote: "There is no such thing as individuals, there are only fragments of families." On a related note the Mikdash Mordechai tells us there is no such thing as community, there are only extensions of families.