What is the most iconic form of architecture in the US or in your country?
One might think skyscrapers but my vote would be for the simple houses built which expanded suburbs after cars became commonplace and highways became omnipresent.
In Canada, possibly Indigenous housing. Instantly recognizable (though seldom currently seen) structures like igloos, teepees or longhouses.
But what says you?
Queen Anne style architecture is very distinctive in the US;
Totally different to the Queen Anne style in the UK
I’d agree with the simple houses in suburbs being the most American but I would narrow it down specifically to houses that are some combination of craftsman and ranch. Not only do they epitomize suburbia, Frank Lloyd Wright also influenced the development of a similar style in a deliberate desire to create something American.
Id like to say the American craftsman bungalow, but it wouldn’t have been possible without the British arts and crafts movement.
Aren’t log houses fairly American in style?
IIRC, we got them from the Swedes who settled Delaware.
I guess the tipi fits the OP. Tents are worldwide, but do any other feature the inner wall skirt that hold in the warmth while funneling the air up out the top?
Mobile Home, Baby! Jack it up, take the axles off and toss them in the corner of the lot to rust and be overgrown with Kudzu, fill up the plastic pool and grab a beer.
As they settle, twist and warp and small gaps open up around windows and doors that allow insects in (especially moths, drawn by the light of the TV that is always on), you and your spouse can fight and argue about unrelated stuff that annoys you. Circle of Life.
On this side of the puddle, for family homes the candidates would be the Federation style
… or the Queenslander
I think in the UK, it’s going to be the Semi-Detached House - a short terrace of two houses (saves on land area, as well as roof and wall construction, still permits residents outside access from the street to the back garden - and most importantly, makes people hate the noise that the next door neighbours make).
(that is, taking ‘iconic’ to mean ‘strongly representative of’)
First thing that came to my mind for the USA is farmhouses.
In the States, those are called duplexes. 
The most American form of architecture on display around the world is probably the Quonset hut.
When the OP said distinctly American architecture, I was thinking more of something like these;
I don’t want to define terms and am happy with what you post. Whatever it means to you.
In western Canada, those are duplexes. In eastern Canada, they are semi-detached.
In eastern Canada, a duplex is one apartment sitting atop another, in one house.
I agree. As someone who has looked at a million photos of rural houses I cannot even hazard a guess as to how many there are. Here is what I consider the typical traditional farm house composed of two rectangles at right angles to each other: Cities, of course, are a different story.
Do other countries have churches like this?
American, here.
Yeah…yeah I was going to go with “McDonalds,” too.
Kind of Winnemacean, I guess. It’s like the T-34 of architecture: it’s not the greatest, and maybe it’s not the best thing that they were built in in the first place, or under the best circumstances…but, by god, we mastered the hell out of making the damned things!
This style of suburban development is distinctly American, as embodied in countless TV shows and movies. It appears in other places in the world but only as a distinct aspirational homage towards the American original.
Cape Dutch, no question.
For the US? Skyscrapers were my first thought, but they’re not actually one unified architectural style, you could have Art Deco or Brutalist or Bauhaus skyscrapers.
Then it hit me: Googie is the most American of architectures. Note how two of Smapti’s 3 fast food restaurants partake of it.
But that development style can have different architecture styles for the houses in it, from one development to another.