The US Civil War (1861-1865), for the simple reason that Americans were killing Americans.
Civil War
http://en.wikipedia.org/wiki/United_States_casualties_of_war
In terms of human lives it cost at least 130,000 Okinawan civilians, 100,000 Japanese soldiers and about 12,000 US American forces (plus 50,000 wounded).
Nips (short for Nipponese), or Japs were the primary terms. I'm sure other terms that were derogatory were used, and these varied from place to place.
In terms of lives lost, 106,207 American soldiers were killed in the pacific theatre of WWII, aproximately 1/3 of all American war deaths. The USA spent at least $341 billion total on WWII.
(Union) Bluebelly (Confederate) Johnny Reb
That soldiers be allowed to keep horses for farming
Russian soldiers
Rifled barrels - in small arms and artillery.
It certainly convinced US war planners that any attack on mainland Japan would be costly in terms of American lives.
Russia 10 million soldiers 25 million civilians China 3.5 million soldiers 20 million civilians Germany 5 million soldiers 7 million civilians Japan 2 million soldiers 3 million civilians Poland 250,000 soldiers 5 million civilians
Answer In terms of American lives, the Civil War was more costly. Americans were not involved in WW1 but for only 1 year.
Russia .
Germany Japan and Russia .
In terms of human lives it cost at least 130,000 Okinawan civilians, 100,000 Japanese soldiers and about 12,000 US American forces (plus 50,000 wounded).
Barbarian wars and invasions of Empire territory of course were costly. It drained Rome's resources in terms of lost lives and the cost of the logistics involved. When Rome was the "invader" of course the offset was the booty and new wealth their expansion created.
Nips (short for Nipponese), or Japs were the primary terms. I'm sure other terms that were derogatory were used, and these varied from place to place.
Adding together the terms and dividing them by the number of terms gives the arithmetic mean.
the cost in lives was many many deaths