As a USA-based company, with our office located in Dover, NH, we have performed SEO services for many national and international clients.
There are differences between performing search engine optimization for a business that is looking to achieve results nationally, that isn't the same as local businesses trying to grow in one particular city or region. Some businesses aren't local; but need to reach more visibility online throughout the country, and might not necessarily care about international traffic; e.g. a retail store that only serves the united states.
We have a process in place for these types of businesses needing SEO on a national level. Since we actually live in the USA, and don't outsource our work as many providers do, it gives us an edge in terms of how we work with clients, and how we are able to achieve results.