Alternative word spelling and date format used by Americans

I'm aware that this is most likely a frivilous question to be asking in this forum but nontheless one that's always had me wondering ... why is it so ?

I'm a native English speaker originally from the UK and wondering when and for what reason and by who's decision did certain words and the manner in which dates are formatted get altered in the US ?

The words I'm querying are specifically ones that in the original contained the letter "u" but eventually in the American version of the word, that letter was removed for some reason.

Some examples:

colour --> color
neighbour --> neighbor
tumour --> tumor
favour --> favor
savour --> savor

Now as for the date format, originally it was DD/MM/YY which is the way it's still used in the UK, here in Australia and many other countries. And yet at some point in time, someone in the US made the decision to exchange the DAY and MONTH resulting in a MM/DD/YY format.

Can anyone shed any light on the above and explain the reasoning behind those changes ? I'm assuming that there had to be a legitimate and genuine need for the changes.

Here's a good explanation for the spelling differences.

Color vs. Colour - The Great Spelling Battle

As for the date formatting, it seems to be mostly localized preferences.

I was curious about the date too.

It turns out that in the UK we say

fifth of July

and most Americans say

July fifth

So it's worded how it is said.

Lets not forget the "customary" system as opposed to the metric system. The word custom is actually put right in there to remove any doubt that it may have a scientific backing.

When it comes to the spelling, all languages eventually develope splits within their native speakers both in spelling and grammar. As such, I doubt you've ever heard the four word super contraction (I'm'a) in the UK or Australia.

I am going to go to the store later.
I'm gonna go to the store later.
I'm'a go to the store later.

What is that, a future tense pronoun or the first steps to deriving a hawaiian language from english?

Despite being raised with the MM/DD/YYYY format, I fail to see how it may have practically come about. Atleast in your model, they are listed in ascending order of time periods. My only guess would be that when flipping through a calendar, the first thing you would sort by is month then the day with the year understood.