The They who said it
Different people will have different ideas about the optimal way to get power, so you can justify pretty much any decision with the villain simply not being entirely understanding of the actual optimal paths.
Generally, taking over a small country is pretty easy. During the cold war, mercenary groups would occasionally march into a country and declare their employer the leader. (See the Banana Republics before the US government got directly involved.)
So if someone wanted to say, invade the Central African Republic for villain reasons, they might do that. It's unlikely there'd be much international response, as long as they could find a patron country who doesn't like the Central African Republic. Probably a regional power, but maybe the US or somewhere like that if they're lucky.
The real question here is how is the villain's organization so secretive if it's really big? Large organizations are proportionally far more vulnerable to leaks, to the point that they can't remain secret for very long. For reference, the NSA in the US officially is not real, but everyone knows it exists. The same is true of Israel's nuclear weapons, for decades it was true of MI6 in the UK, etc. Very quickly everyone would know about the organization. The best bet is to try to take control of a small country as quickly as possible and become a government, so that everyone knows about the "weird dictatorship down the road that's spying on everyone and has a large army so probably isn't worth dealing with directly" rather than the "spooky weird cult with an army that's trying very hard to be secret and failing because it's so big, we should probably deal with it."
As for getting bigger and bigger threats beyond the soldiers on the villain side and why they'd bother, more supporters means more force projection. Sure, you can hold some mid-sized country that previously didn't have a particularly centralized state, but you can't hold more land without more acceptance of your rule, and you can't get that without force projection over more people and time. You can't get that time or those more people without more force to project, so more army and more powerful allies would make controlling more area with more people possible, as long as you're always the dominant partner in the alliances.
And the more territory controlled properly, the more the plan can be carried out.
At least, that's the logic most plan-oriented conquerors tend to have. Ones who conquer for the sake of conquering tend to not bother so much with allies and rely on keeping everywhere they can feasibly control controlled.
While I have posted this in another broader thread here in the past, I still felt that I should give it a try as a thread all its own here as well
Anyways, here’s the deal…
You see the main villain of this fanfiction story wants to control the world in order to “purify it”, “make it better” and other such things, and in his quest to do so, he has spent a great many years building up an incredibly powerful multinational secret organization, complete with a great number of loyal, battle-ready soldiers. However, what i am planning to have as a part of the long-running story arc is that the main villain intends to use various means in order to increase his forces in his plot to takeover. You know, like; recruit or tame incredibly powerful beings and creatures or just use things like magic or science or both to actually create his own versions of the aforementioned. This seemed like a good idea to use as a story arc and a really good way to give my overall story a sense of “something wicked this way comes”, if you know what I mean.
However, what I find to be the real problem here is that; whenever I imagine what the main villain’s evil organization is like, I usually imagine it to be very powerful, very competent, and have a vast army of armored soldiers at its initial disposal. An army that would, at the very least, be able to take over a small third world country, if given the right amount of time, and, the very most, would be able to launch a series of dangerous attacks upon a much larger nation, if given the right amount of precise planning and proper coordination. But if the main villain was already in possession of such an impressive military force of his own (still not so sure about how to how he even got it the first place), then why would he need to recruit and/or tame powerful beings and monsters, much less create them, huh? Why wouldn’t he just use the army that he has in order to begin his campaign?
I mean, I have tried to create an explanation for that; you see, I figured that it would help to say that while the main villain might want to takeover the world, he doesn’t want to start a war, so he intends to bide his time and either A.) create an army that is so big and powerful that the takeover will be as quick and painless as possible, or B.) come up with a plan that will ensure his absolute domination of the world in one fell swoop. Although, to be perfectly frank with you all, I am not entirely certain about just how well that that explanation holds up, any thoughts?