Steven Pinker explains why the Long Peace is a genuine trend. There has been
a superposition of four patterns (p. 192): (1) No cycles; (2) A big dose of randomness; (3) A long-term escalation in the destructiveness of war, which made a substantial U-turn after 1945; and (4) Long-term declines in the frequency and duration of war. Multiplying the trends in (3) and (4) yields the overall decline in war that we call The Long Peace, and Factor (2) should keep us humble and cautious.
This is about right, I think.