First off, you're lucky to have the time and money to take such an epic backpacking trip. The biggest impediment to travel, regardless of where you're from is typically money.
And that relates to the second biggest impediment, at least for Americans, time. The US has no required vacation time. Most employers offer it, but it's usually no more than two weeks a year for younger employees and it is often frowned upon to take the full two weeks at one time other than for using it up before going onto unpaid maternity leave.
My employer is very generous with vacation time, but the workload is so heavy that it requires a ton of planning ahead and catch-up afterwards to take more than a week off.
Last year I spent months getting projects and job responsibilities assigned to others before taking five weeks off to travel. I consider myself very fortunate to have been able to do that as taking that amount of time is highly unusual for working adults in America.
A large part of it is the huge distance of travel destinations.
With relatively inexpensive means, a European can go pretty much anywhere in Europe, and Africa and the Asia aren't terribly far either.
Our close destinations include Canada, which is lovely, the Caribbean, which most use for resort style vacations (i.e sitting on a beach and getting drunk) rather than cultural ones, and Mexico, which is rapidly becoming too dangerous for most fairweather US travelers.
It costs a LOT of money for us to get to Europe, Asia or South America to find radically different cultures.
Most Americans, with their 2 weeks of vacation that they are strongly encouraged to not use, would rather spend it at a domestic destination like the beach or skiing, or go to an all inclusive Caribbean resort.
If you take advantage of all of your vacation/sick days, you will most likely be passed over for promotions or raises, because this is perceived as laziness and not being devoted to work.
Thanks to the economy improving my workload is heavier than it's been in years. So heavy in fact that any trips were limited to long weekends and I'll finish the year with at least three weeks of unused vacation.
Don't forget a lot of employers look at long gaps of unemployment as highly suspicious regardless of reason.
There is a lot of fear about not being able to get a job when you come back from a long trip, especially if it's a career. I've seen quite a few people say that they wouldn't hire some one that went traveling for a year because they probably aren't reliable or they might do it again.