The Boorman Treaty is an agreement signed by all four Major Houses that forbids direct conflict between the Houses. It is likely that this treaty was made in the aftermath of the 80 Years War in 700 AS. Kusari (rightly) accused Rheinland of violating the Boorman Treaty by building up its military along the Kusari/Rheinland border during the Single Player Plot. Later, in Mission 5, Rheinland blockades the Omega 7 system, which Juni says is a direct violation of the terms of the treaty.