It would a stereotype to see a short UK Police officer dressed in a Black Getup reminiscent of the 1940's with no firearm, only a rape whistle. Then with a sign behind him that says "NEED HALP WITH WORLD WARS. UNITED STATES, U THERE BRO?"
If this is a stereotype where did it come from? Some stereotypes can be more offensive than others. Let's look at these:
Short UK police officer? Minimum height in most UK forces used to be 5'8" and in some forces it was 6'.
Black uniform? It's always been dark blue.
No firearm? Firearms were never needed here, with strict gun law criminals rarely carried guns, 3/4 of UK police officers back in 1975 would have resigned rather than carry firearms (based on a survey by the Police Federation). Times have changed - but I won't go into the current situation.
Only a rape(?) whistle? You're thinking of the days before personal radios, the US police didn't have personal radios either before they were invented, if you look at old US B&W movies you'll see the cop with a whistle.
Need help with world wars and calling for help? I think you need to study some history from more non biased viewpoints. The US entered WW1 in 1917 (Europe had been at war since 1914) for several reasons, one being that Germany sank the SS Lusitania, a British passenger liner with US citizens aboard and also sank a number of US merchant vessels; a second was the Zimmerman telegram in which Germany offered Mexico an alliance to attack the USA and a third was that the US had sold so many armaments to the allies on credit that they were afraid the US economy would collapse if Britain and France lost and these debts (with interest) would thus not be repayed.
As for WWII - it took Pearl Harbour to bring the US in in Dec 1941, the war in Europe started in 1939. The battle of Britain (the pivotal point in WWII where Hitler failed to destroy the Royal Air Force {a significant number of Americans served in the RAF as volunteers before the US entered the war} and was forced to give up his plans to invade Britain) was over by October 1940. Hitler then made the fatal mistake of invading Russia 6 months BEFORE Pearl Harbour.
I'm not denigrating the part the US played in either war, just pointing out some facts that don't usually make high school history classes. Both wars
could (not neccesarily
would) have been lost without US intervention and the world would be a VERY different place if this was the case. If the Axis powers of Germany, Italy and Japan had managed to seize control of the rest of the world I very much doubt if the USA would have survived on its own for long. The arrival of the US forces with their huge manpower and economic backing certainly made both wars shorter and ultimately saved lives but in both cases it was neccesity, not altruism that brought the USA in.