How did Truman's decision to use the atomic bomb forever change the nature of international relation?

From the time that the US used atomic weapons against Japan at
the end of WWII, the nature of international relations was changed. This was because all of a
sudden a war between major powers had become much more horrible of a prospect than it ever had
been before.

Before the advent of atomic weapons, war was simply
another part of international relations. Even major powers were relatively willing to go to war
with one another. After atomic weapons were invented and used, it was no longer anywhere near as
feasible to have a major war. Everyone knew that a major war would become a nuclear war, with
disastrous consequences. This changed international relations fundamentally because it removed
war as a serious possibility among major powers.