Sengoku's actions at Marineford

The whole was at marineford, at least from the World Government's point of view, was to end the Gol D. bloodline. When Roger was executed, they hunted down any women and child who could possibly be connected to him. He disbanded his crew, knowing what their fate would be, so that they could live in peace and carry his will, rather than be hunted because of their roger ties. The Cipher Pols even went after Tom, for building Roger's ship.
So why is it that Sengoku negotiated with Shanks and...

Sengoku's actions at Marineford