Seo For Website

Does SEO work on the website of a country or the world works?
Just something I want to try to clarify and I wonder if anyone can help with this. Does SEO work on a market basis only, ie a UK site SEO only good for the UK market, or captured many markets at the same time. If the event is that SEO works primarily on a market-based one, what is the best way to do it, "multi-market"? Finally does anyone know how it was determined that a site is a UK site or U.S. site?
seo brings our website ranking in search engines, which engines search not for a certain country or certain regions global access to anyone we have to put our website in the top 10 through the link word search key to seo.
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