The most serious blow to president johnson's vietnam policy:

The correct answer is was the Tet offensive of 1968.

People in the United States didn't know much about the Vietnam war and believed that it would be an easy victory for the Southerners and the US troops. When the Tet offensive happened, it was revealed just how much a of a problem the war was and how the United States was unable to deal with it and people started turning more and more against the war effort.

Edefeated the swedes to gain control of the land along the baltic sea, and he signed a treaty with china to gain rights to lands north of manchuria.is  did peter the great expand russia’s borders, it took palce afetr battle of poltava in ukraine in polish-lithuanian commonwealth