WWII had a bigger impact, on the whole.

The second World War left more than 3 times as many people dead as the first did. Everyone thinks about the Holocaust killing six million Jews, but it also killed more than 10 million others, and the war in total left 60 million people dead. That's more than the population of many countries! That's more than the population of the continent of Australia!

Not only this, but the technological advancements were astounding. RADAR first came about in WWII. This was huge! It was the first war where massive amounts of aircraft could be reliably used to completely annihilate populations. WWI aircraft were shaky, unreliable, and veritable death traps!

WWII had massive impacts all over the world. While WWI's aftermath consisted largely of lots of treaties falling through (think of the Treaty of Constantinople) and lots of land getting mixed up in confused ways, WWII saw the world's superpowers take land and distribute it as they saw fit! You saw the winners of the war clearly make a global statement of "you lost, and now you will comply with our demands" with very little attempts to politically sugarcoat the situation.

WWII saw the a massive scale systematic and industrial execution of an entire race, almost without public knowledge! This was simply horrifying. Even though public opinion of the Jews was by no means friendly, most could not even comprehend the sheer scale of death that was being discussed as a fact of the last half-decade.

WWII also brought about the advent of nuclear weapons. Never before had human kind been able to use a single plane to wipe out hundreds of thousands of people, and level entire cities. This was a war that consisted of dozens of bombers flying over a city simultaneously. People could not help but imagine what would happen if this tactic was repeated with nuclear weaponry.

Finally, WWII saw the world clearly divided into two separate sides with two separate super-powers facing off, while much of the rest of the world rather sat back and just hoped they didn't destroy each other. Go look at other conflicts that happened post-WWII, I am specifically thinking of the 6 Day War in the Middle East. Conflicts became a massive game of chicken, where countries looked for how much they could gain, lose, or destroy before attracting too much attention from the world's new-founded superpowers, the USA and the USSR.

WWII has had a larger impact on history than any other war before it, or since.