D4 Treaty, or simply called The Treaty was an agreement signed between the major factions in 2013, preceeding the events of S.T.A.L.K.E.R. 2: Heart of Chornobyl.
Background
Following the events of Call of Pripyat, there was a need to make peace between the warring factions of the Zone, presumably in preperations for Operation Zenith to the Generators.
The following is a report about the outcome of the treaty. While the author and recipient are redacted, it is assumed that the report was sent to the Regulatory Board by Dr. Dalin.

I propose that we set a date for a face-to-face meeting to discuss our next steps regarding newfound "allies", namely:
1. Supply chain logistics
2. Assignment of responsibility for control and collection of data
3. Planning of operation Zenith
4. Recruitment of field agents from among the illegals
5. Personnel changes in Ward structure
The treaty led to Duty being forced to transfer Rostok to Freedom. Both factions were barred from fighting each other directly, so they begun a proxy war by supplying allied bandit gangs in Garbage, one led by Roosevelt, the other by Shah. Over the years, Duty's strength and influence waned, while Freedom set up a highly successful trading hub in Rostok.