It's really quite simple to invade a country. Send a single, solitary soldier there without permission of that country's government and there you go, you've invaded. This gets a bit more difficult the more remote the country gets, but you'd be hard-pressed to find a more difficult country to invade than New Zealand by this standard.

Now, yes, that's an extremely pedantic answer to the question and if you're not satisfied with it, congratulations, neither am I. However, I did open with it for the very simple reason that it illustrates a key point: what definition of "invade" are we using here? If we mean it in its most literal sense, then the above paragraph stands. If we're attaching implications, then we can go on for a longer time.

Also, for that matter, we have to ask the question of "who's invading?" For example, if we are asking "how easy is it to conquer[1] Lesotho?"[2] the answer is "if you're the Republic of South Africa, very easy, and if you're not, then as easy as the Republic of South Africa allows it to be."

Having gotten through all of that, let's lay out some ground rules. First, we aren't looking to merely invade, but neither are we really looking to completely overrun, either. You don't need to completely overrun a country to conquer it, and once you've won, what's the point of keeping going? So what we're really looking to do here is to stage a successful invasion that beats the other country into submission. As per the question details, we will not be taking into account the current readiness of any given state's military, and instead will purely be taking geography into account - geography in this case being taken to mean "sociology, infrastructure and topography." We shall also assume that any neighbors of that state will give you free military access so that you don't have to worry so much about staging from halfway around the world.[3] And last, we won't talk about the subsequent occupation, because you're looking to successfully invade and get concessions in a peace treat, not necessarily invade and annex.

An obvious candidate from history would be Russia. Russia has a great many advantages in beating back invaders. First, it has unrivalled strategic depth, which makes invasion a logistical nightmare. Second, the weather ranges from mild to "cold enough to freeze the balls off a brass monkey,"[4] thus necessitating all sorts of winter gear to be specifically designed and supplied during the invasion. Third, the infrastructure in the middle of the country is massively underdeveloped reinforcing the logistical nightmare. And as for invasion routes - you can try going through the Caucasus, but those mountains are fairly easy to play defense on, and since the area also corresponds to Russia's oil fields, bet your bottom dollar it'll be armed to the teeth. You can try going through the Steppe, but that means your resupply costs will be through the roof before you even cross the Russian border: good luck finding the food and water needed to keep an invasion army fed in the middle of Kazakhstan or Mongolia. You can go through the Pacific Coast, but after Vladivostok, there's a lot of Siberia before you hit Russia's centers of industry.

Which means you have to take the same route Napoleon and Hitler did. So, you know, if you're willing to bet you're more clever than Napoleon or that the Russian administration at the time of your invasion is even better at hobbling the army than Stalin was, go for it. I wouldn't.

Strategic depth and few good invasion routes describes a large number of other countries. The US and Canada have already been mentioned, and China, being surrounded by the Himalayas and the Gobi Desert essentially forces invasion through Korea (or else, shudder, a gigantic amphibious assault that would make D-Day look tiny) so yes, that would also fit the bill quite nicely. You can also go the remoteness route. I haven't shut up about New Zealand yet, but Australia would also be a nightmare to invade, Here's some analysis on that: Harold Kingsberg's answer to How do I invade and conquer Australia?

But let's take a break from depth and remoteness for a second and go for a somewhat less likely candidate. Now, I wouldn't argue that the country I'm about to state is the hardest to invade (I'd rather try invading it than invading Russia or China, for example), but it certainly punches above what you might think its weight is: Japan.

The Japanese Home Islands have never been successfully invaded. Now, in the case of World War II, this is because Japan surrendered before such an invasion could take place, but we do know what the plans for that invasion looked like. It was called Operation Downfall and it came in two gigantic amphibious operations. The first, Operation Olympic, would have been the invasion of Kyushu. The second, Operation Coronet, would have been the invasion of Honshu from the Kanto Region. Here's the thing: the Japanese pretty much knew what Olympic and Coronet were going to look like. They knew where the landings were going to take place, because if you're going to land an army on the Home Islands, those two are the only good landing zones.[5] The result was that blood was very much expected: the estimates for casualties in Operation Downfall came out to about 1.2 million soldiers. This would have been more casualties than the US suffered in all the historical war.

Japanese culture has changed substantially since those days, but not entirely. Point being, I sure as hell wouldn't want to invade.

[1] Note the deliberate change in terminology here.

[2] Lesotho is a small, landlocked African country completely surrounded by the Republic of South Africa.

[3] Unless, of course, you're trying to invade New Zealand, at which point you're pretty much forced to invade from halfway around the world.

[4] Which is a great expression, but actually greatly understates just how cold Russian winter can get.

[5] Which actually means that Operation Downfall shared several elements in common with the attempted Mongol invasion six hundred years before.


Source: https://www.quora.com/Which-country-is-the-most-difficult-to-invade

Neteller here: www..com.ng

Germany as far as am concerned. Their international passport and visa is so difficult to come by even to its own citizens let alone other nations.

Germany is such a jackass country, it may not have volume of weapons like America.and Russia but its defence is one of the best in the world.

Germany is sophisticated, don't take it for granted.

https://www.youtube.com/watch?v=8qXZp8bxpNY&list=PLUYBkB2xV-uVAtu5WJeNMnU8ne0jN9HPF

Sai Russia!

Would be the PanAfrican Federal Nation.