Considering your other question, citing you like history and what to know more, perhaps WW2 should be the place you start considering your lack of knowledge highlighted by the above.
"only major contribution ... Hiroshima and Nagasaki ... a rouge German scientist."
Yes, the Manhattan project was a joint project, however you should also consider who provided the funding and facilities needed.
"... contributed the most soldiers towards d day ... Russia's sheer numbers and rellentlesnes,"
The US provided the most soldiers on the Western Front following "D-Day". Allied strategy in Normandy involved the Anglo-Canadian Army pinning down the Germans, to allow the Americans to break out and facilitate the rout of the German military in France. We Brits, and the Canadians, lacked the manpower to do it alone or man the entire front.
You should find out the difference between the Soviet Union and Russia. The Belorussian people were the ones who suffered the most during the war on the Eastern Front not Russia or Russians.
"Britain's non stop bombing raids ... French ... large contribution ..."
Initial RAF efforts were far from effective. Even the spectacular damage done by the 'dam busters' did little in the overall scheme of things. It was the combination of Anglo-American bombing, focusing on transport and oil facilities that started to do the most damage. Unfortunately, that was more towards the end of the war.
It was other factors, rather than the air losses suffered during the Battle of France, that resulted in the break of a few weeks between that and the Battle of Britain. The break or the losses suffered, where not what resulted in the German defeat.
"... Canada ... objectives at d day, ... responsible for delivering supplies ... d day would never of happened,"
The Canadians failed to take all of their D-Day objectives although yes, they pushed the furthest inland. It is also interesting to note, if I am not mistaking beaches, that Juno contained a German bunker that refused to surrender for several days.
As for the supplies, you cannot just magically discount the American aid that was also put into making D-Day happen or the British effort. It was a joint operation and jointly funded and supplied.
"... Canada was the liberation of Holland ... helped France ... to go back on the offensive"
No. For starters, it is The Netherlands not Holland. Holland is an area within The Netherlands. The Netherlands were not fully liberated until the end of the war. The Anglo-Canadian efforts in the Netherlands had little to do with the French bringing men back to the battle.
"... Poland ... enigma code and polish air forces ... battle of Britain."
Partially correct. Polish agents provided France and Britain with a great advantage, but it was Bletchley Park that had to crack the updated German encryptions. Did you know American volunteers also took part in the battle, via the Canadian Air Force?
"what major contributions did America actually make other than obvious numbers?"
*Lend-Lease, provided to all of the Allied forces, the Soviets, and the Chinese.
*Led Operation Torch, which brought about Vichy France switching sides
*The re-armament of the French military, once Vichy forces switched sides.
*The strategic bombing of Germany and Japan.
*The major naval battles that crippled the Japanese fleet.
*The submarine campaign against Japan that crippled her merchant fleet.
*The island hopping campaign that pushed the Japanese back, stopped the Japanese drive on Australia, and liberated various islands and the Philippines
*Aided in the Battle of the Atlantic
*Provided the most troops on the Western Front
*Provided the majority of resources needed for the successful completion of the Manhattan Project
" if they waited 2 months ... China would know their place."
China was an ally, and not the same regime that is in power today. The war had not ended, had the Americans not dropped the bombs, the fighting and death would have still carried on via aerial bombardments, in China, South-East Asia, and the Soviet Army overrunning northern China.
"you deserve no honor for it."
Neither does *our* (the British) aerial bombardment of Germany.
"@artic wolf ... is my knowledge from what I have previously learned"
None of your facts are actual facts. You need to go back and study the subject, because your knowledge of what has happened is superficial and limited.
As for your actual question. People, as you highlighted, have a superficial understanding of what took place. Nations tend to highlight their own contribution. Some Americans, like my in-laws, like to poke fun and do not mean it, as Brits do towards Germans. On the whole, blame the entertainment industry: it tends to focus on the American point of view.