The Vietnam War claimed 50,000 U.S soldiers and cost the U.S $200 Billion.
Do not know if this is the most costly (I suspect it isn't), maybe others can add to this answer with similar stats for other wars.
Additionally, this is only the cost from the American side. The real cost of the conflict must be far greater.
Actually the Vietnam "War" is techniacly and legally refered to as a "conflict" as we lost it, this way the US can claim it "has never lost a war", kind of pathetic if you ask me. Any way, the most costly single battle in American history was the Civil War Battle at Antietam, followed closely by Battles such as Gettysburg, or the Battle of the Bulge, but the single most costly conflicts would be World War One or Two, Im no WWI expert but the Battle for the Somme is one of the most famous WWI battles fought. I do know alot about WWII, and in particular the Battle for Stalingrad shines out, with over 1 million men KIA (killed in action), missing or injured on both the Russian and German sides by the time it was all done (but that's count the entire campaign for the city, from the first German advance towards it, to the fire bombing of the city, to the actually seige, and finally the Russian breakthrough and encirclement of the Germans) others to consider would be, as stated, the Battle of the Bulge, as well as the D-Day landings, and subsiquent battles that followed to open the door to Europe, especially the Battle for St. Lo. In the Pacific Theater major battles included Okinawa, Iwo Jima, Guadalcanal, the Solomons, and both the battles for the Philipeans.
The War of The League of Augsburg
Yak 3,perhaps
they might of had to fight, as percentage of population most costly war on us soil.
$40,000
While the B29 was expensive it cannot even compare to the real most expensive project of World War 2. The Manhattan Project was the most costly project to develop the atom bombs used in World Wa2. This project cost well over 2 Billion Dollars in the 1940s. That would be like a 20 Billion or so dollars today. So the atom bombs each cost slightly under a billion dollars a piece.
It was very costly.
World War II
The War of The League of Augsburg
Both the War of Independence and the Yom Kippur War were much more costly to Israel that the Six Day War.
brutal, bloody and costly both in lives, injuries and cost......
The Civil War battle of Sharpsberg as America's most costly battle whit about 23,00 casualities.
Yes, the Vietnam War.
You should try more research.
Second Seminole War
In warfare the war which is most costly to US lives is the US Civil War.
Yak 3,perhaps
they might of had to fight, as percentage of population most costly war on us soil.