I understand this is a bit of a doozie of a question, but are there any historical factors that contribute to "American pride"?
Jumping into something that isn't necessarily a historical topic, I think it would be better to rename the topic, because the particular thesis in the topic itself is one that isn't necessarily accurate. I think it's fair to say that America is more publicly patriotic and nationalistic then many European states, but having just returned from East Asia, where it is literally a crime in many countries to not say that the nation was great, I doubt the general accuracy. Youguv did a poll about a year ago that bears this out. China and the US were about equally in terms of "proud to be" responses, and Thailand beat both.
I think the arguments for this are actually historical.
First of all, the term Patriotism. Although the word is derived from the Latin for "father" by way of the French. The earliest citation of the word Patriot to define "American nationalist" was in a letter from Benjamin Franklin before the revolutionary war. So when you say "Why are Americans more patriotic", it's partially because the term literally has come to mean American nationalist.
I think in this case, you can substitution nationalism for patriotism.
American Patriotism and Exceptionalism pretty much predates the founding, starting with "the city upon a hill (https://en.wikipedia.org/wiki/City_upon_a_Hill)" which posited that America had a unique roll to play in the nations as a example of Good in a otherwise corrupt/sinful/royalist world. The introduction of the constitution, as well as the bill of rights as well as American Democracy not falling down like every other country predicted continued to build a sense in America of a manifest destiny and a special role, unique identified with the nation state. What that role has been has changed over the years - first because it was a refugee for religious refugees, then as "the child of the enlightenment", and "the arsenal of democracy". America viewed itself as something different and apart. When America was founded, it was founded on the concept of being a nation of many people who shared a common ideology and a common goal. Therefore the founding of the nation itself stood for being American in a way that simply being a member of a state in Europe did not always.
You can see this in the French Revolution as well. Being French during and after the revolution was not about being ethnically French, but instead about the Rights of Man, and the French Culture. Napoleon leveraged this heavily as part of his justification for the Napoleonic wars. The British and the dutch saw empire and commerce being uniquely of their nation, and it's patriotic mission as bringing civilization to the masses, and at the height of their empire, I have no doubt that British Imperialism was a stirring thing, and Winston Churchill would certainly agree.
The other historical change is that large parts of Europe eschewed nationalism after World War I and world war II, where nationalism was a key contributing factor to the devastation of Europe. Hitler embraced the (pre-existing) concept of "Volksgemeinschaft" which was a mythical blood union of all Germanic people, no matter what nation they may currently reside in. A greater Germania. That nationlism, as well as the nationalism in Italy and the Soviet Union, played a special role in the unpopularity of nationalism in Europe due to the legacy of Hitler. Once Hitlerism was defeated, it led to a concerted effort in Europe to break down state barriers, and to create the EU superstate. Since 1957 that superstate has been predicated on the concept of a "ever closer union" which necessitated the breakdown of the state, a goal of which nationalism directly opposes.