The total number of casualties in World War I, both military and civilian, were about 37 million: 16 million deaths and 21 million wounded.
WWI lasted 4 years.
World War II casualty statistics vary greatly. Estimates of total dead range from 50 million to over 70 million. The sources cited on this page document an estimated death toll in World War II of 62 to 78 million, making it the deadliest war ever. When scholarly sources differ on the number of deaths in a country, a range of war losses is given, in order to inform readers that the death toll is disputed. Civilians killed totaled from 40 to 52 million, including 13 to 20 million from war-related disease and famine. Total military dead: from 22 to 25 million, including deaths in captivity of about 5 million prisoners of war.
WWII lasted 6 years
The Korean War dead: US: 36,940 killed; PVA: 100,0001,500,000 killed; most estimate some 400,000 killed; KPA: 214,000520,000; most estimate some 500,000. ROK: Civilian: some 245,000415,000 killed; Total civilians killed some 1,500,0003,000,000; most estimate some 2,000,000 killed.
Korea lasted 3 years.
The lowest casualty estimates, based on the now-renounced North Vietnamese statements, are around 1.5 million Vietnamese killed. Vietnam released figures on April 3, 1995 that a total of one million Vietnamese combatants and four million civilians were killed in the war. The accuracy of these figures has generally not been challenged. 58,226 American soldiers also died in the war or are missing in action. Australia lost almost 500 of the 47,000 troops they had deployed to Vietnam and New Zealand lost 38 soldiers.
Vietnam lasted just over 8 years
As for both Iraq wars and Afghanistan estimates run from less than 500,000 to just over 1.5 million. This discrepancy is due primarily to different criteria for "war" deaths being applied for political, practical and organizational, agenda driven desires.
These wars have lasted 9 years.
It looks like as war gets more modern, casualties have decreased dramatically.
(If WWI had lasted 2 more years casualties could potentially have been comparable to WWII)