but to help maybe you can corroborate the following:
there is an ancestral lineage to the founding documents and frameworks of countries, with branches also connecting and merging
most countries in the form and shape that we know them today have had a major revision in or replacement of their constitution over the last 100 years. so even though people say the US is "young", many old world countries are younger or are operating under a framework which is much younger
when people say the US has been exporting democracy, this would be true. The US has a habit of creating temporary vassal states without really taking any resources or expanding its territorial boundaries, thats kind of new on the world stage, and in parallel the concepts have been inspirational to other states.
and of course its not all related to the US and supernational institutions as it all evolves in parallel, but they do all influence each other.
Where can I read more about this in short-form (not a college Politics textbook).