The Vietnam war which was meant to stop the spread of communism or Iraq and the war on terror, for me the Vietnam conflict wins hands down as however misguided and badly executed communism may be, it's a peacetime movement that is inherently democratic, and to send young men to their deaths solely to try and stop a political movement gathering momentum because you fundamentally disagree with their values is the work of the devil.
http://news.stanford.edu/news/2010/september/naimark-stalin-genocide-092310.htmlStalin killed more of his own people than Hitler ever did....communism was and is a nasty regime that to this day shows there real traits on a regular basis.
Only recently a certain Korean gentlemen wiped out family and friends because they were not a big fan of his way of ruling which is...well communism.
That said what has the recent war in Afhganistan proved...the Taliban seem stronger than ever which make it incredibly tragic that around 500 British troops have died...was it for nothing?
The Boer war between the Afrikans and the British was the first real modern war along with the tragedy that was the Crimean war.
The first World War for some reason is the war that is remembered as a hideous piece of modern history...it was because of the modern methods used by a few generals on all sides to use men as canon fodder on a momentous scale....incidently at the wars end around 1918 another 20/30 million people perished from the deadly Spanish Flu that spread around Britain and Europe.
So now to answer your question and this of course is just my opinion....for me WW2 was the most hideous war on account that just 20 odd years after WW1 the same happened again with even worse consequenses for millions of INNOCENT people not soldiers....Jewish civilians who never raised a finger in anger...the Romanies were wiped out almost...who did they ever fight against.
Clever people and Homosexual people killed for what they were....not because they were soldiers.
We are lucky in a sense...people born around the 1900's had two World Wars to live through(if they were very lucky)..and then in older age must have looked on with amazement when Vietnam came around....some may have been around to see the folly in the Falklands.
War is never far around the corner for any nation which brings me to a completely different question to the Scots who desperatly want independance.....in two world wars the home countries stuck together like glue under the UK banner to fight wars....millions of them died.
Have Scotland thought of this if in 200 years time a manic dictator decides he likes there whiskey...will they have there own army to defend itself....or will it rely on the UK for its defence.
Think we all know the answer to that one which makes the meaning of the word Independant rather strange...because in essence they never will be.