One of the essential elements to the success of large scale evil is the dehumanization of your intended targets. This allows you to direct the will and effort of large populations against other people with a minimum amount of resistance.
"Why would we want to do this?" you ask. Simple. For the payout.
First, it enables you to take whatever resources your targets may be sitting upon. Africa has diamonds, gold, and other precious metals and minerals. The Middle East is rife with oil. South America has oil, medicinally useful plants, and fertile soil. North America has fertile farmland. Asia has farmland, oil, forests, and minerals as well. Europe also has great farmland, and mineral deposits.
Second, harvesting resources can be messy and destructive, rendering the surrounding environment uninhabitable. Pillaging a distant land keeps the mess away from where you live.
Third, conquered people make great free or cheap labor. Building robots to build all of your stuff is expensive and a hassle to maintain. Dehumanized people are cheap, and no one cares enough about how you treat them to really do anything to stop you. Look at how many middle class religious people use iPhones, shop at Walmart, and buy clothing made by virtual and/or actual slaves in Indonesia. This is despite very public incidents of clear human rights issues that resulted in hundreds of deaths.
So, how do you go about dehumanizing people?
First, you isolate and bring focus to the differences they have from the people you are manipulating. It's easier if there is a difference in skin color, or if they speak a different language. These are obvious differences that even children can reliably identify. Lacking these, the next major difference to target is religion. People will actually volunteer for persecution for their religion. They think it makes them special.
Next, you convince your rubes that they are superior to your targets because of their skin color/language/religion/hair color/shoe size or whatever. This is the easiest step, because everyone wants to believe they are special. Your rubes will rapidly internalize that feeling of superiority, and will begin helping you create rationalizations for why they are superior, and why the targets are inferior.
Third, label your target group in such a way that it reinforces their status as an outsider. America is actually quite good at this. European-Americans are always just Americans. Everyone else is a something other than an American, i.e. Asian American, African American, Native American, etc.
You also give them derogatory names, which may or may not make sense. One to two syllables words should be used, preferably words that children can rhyme with things.
Fourth, make your rubes afraid of your targets. Fear is the primal force that motivates people to action, and it shuts down rational processing. If you can instill fear of your targets into your rube population, you can get away with the most vile acts, and no one will stop you. You're mad scientists will love you for providing an endless supply of test subjects.
How do you accomplish this? Lie.
Tell your rubes that your targets will rape their women or molest their children. Tell them that they are violent sociopaths, bent on the destruction of their way of life. Find a few actual examples of criminals among your target population, and blow those way out of proportion. Portray your targets as criminals and terrorists in a constant barrage of media. Images you use should make your targets seem less intelligent and aggressive. If you tell your lie loud enough and long enough, people will believe it.
Once you've accomplished this you can plan your invasion, and reap the rewards of exploitation for generations. Enjoy.