Each person has his or her own criteria for what "counts" as having been in a country. Some simply need to step foot on foreign soil; others feel that they ought to travel around for a bit. I'll tell you that personally, I won't consider myself having been in a country, unless I stay at least a week or two. When I was thirteen, I visited Canada for a couple of hours. I also stopped over in Norway on my flight to Thailand. But if someone asks me if I've ever been to Canada or Norway, my answer is no. I feel as if I need to be in the place long enough to acquire a moderately good understanding of my surroundings. For most places two weeks is my minimum.
There are, however, exceptions. A few very small countries exist, where two weeks would be overkill. For example, after Vietnam I plan on visiting Singapore for a week. For those of you who don't know, the entirety of Singapore is smaller than New York City! There are even smaller countries you can easily walk across (Monaco, Nauru, etc), where a day or two may be plenty. On the other side of the spectrum, huge countries such as Russia, China, Canada, and the United States exist. I think I'd have to give each of those countries at least six months apiece. Heck, when I go to India I'll be spending a minimum of two months there.
Then there's the question of what is considered a country. It's all a big political game: everyone has a different list of what they consider countries. Generally, I use the UN's list, but only to keep things easy for myself. Just because a place is not on the list, does not mean I don't want to visit it. Although, Taiwan, Kosovo, and Somaliland (among many others) have limited to no UN recognition, I'll probably still explore them someday. And even though the United Kingdom is technically one country, I'll definitely visit all four areas (England, Scotland, Wales, Northern Ireland) when I go. Then there's the question of government owned territories, such as Puerto Rico and Greenland. Sure, they're technically parts of the United States and Denmark. However, they are definitely "different" enough from their respective countries, to warrant individual visits.
If you compiled a list of all the different areas that anyone considers a country, you'd probably have between 300-400 places to go. The United Nations currently recognizes 193 countries, so that is a fairly easy starting point. When I have visited all 193 countries, then I'll start focusing on the other 200 or so. Hefty goal, right? That's why I'm starting with as small of a number as possible. As it stands, I'd have to visit an average of 3-4 countries per year for the next 50 years! However, I'm not doing too badly. By the time this trip ends, I'll have already visited
8-10 countries from the list! At that rate, it would only take 20 years to see every country ;)
Really, most of this article has been me having fun speculating and musing. I don't want to give you the impression that I'm traveling the world just to "collect" countries. The true joy of travel comes from the journey: both outward and inward. It's more about seeing places that interest me than it is about ticking off check-boxes.
But I really, really want to visit every country in the world!