I was thinking about how aliens IRL would arrive and interact. Most likely arriving in spacecraft with Alcubierre drives, and using ion engines powered by fusion reactors for efficient space travel. They have no shields, since that's impossible, but they know much more about warfare than we would. In addition, they have artificial magnetospheres around their ships to deflect radiation, but thats just a technical matter. Their ships will also be equipped with Stanford toruses and will be modular in nature. However, they do not need many of themselves to control their fleets, since they also have advanced AI ships tagging along.
Their motives for arriving may vary, but most likely not even visiting us in person unless they need a new planet to colonize. They would have sent probes disguised as asteroids on an elliptical orbit that will pass by Earth, which would easily fool us into thinking they're just metallic rocks with some silicates. Arriving on Earth and kidnapping humans for experiments is just too risky from a strategic standpoint, as they want to arrive in a surprise attack next.
Once they discover that Earth is suitable for colonization, humans be damned, they will arrive with a small fleet of warships first before sending their colony ships. They don't want their civilians killed en-route by human defenses.
Next up, the aliens detonate many nuclear bombs all over the Earth's upper atmosphere, effectively wiping out the electronics of countless nations. The USA, Europe, China and other major powers are hardest hit, since they use electronics to make things efficient. It will also knock out military defences in a similar manner.
Nuclear-capable nations all over the world, operating on whatever electronics they have left after EMP attacks, attempt to use their nukes as a last resort, including from submarines. The aliens simply evade the nukes by simple orbital maneuvering, since they can detect and plot trajectories of many incoming nukes just like human radar systems. The nukes that did not detonate harmlessly in space fell back to Earth and cause more human casualties.
At the Earth's surface, there is general panic and mayhem. However, some locations such as African nations are less affected due to them retaining simpler lifestyles and less electronics usage, although they have much less defences to start with. Also at this point, the militaries around the world have declared martial law and are attempting to figure out backup plans. Religions try to figure out how to deal with a full scale alien invasion that's seemingly perfect so far, but the religious would quickly identify them as demons or other evil entities, or simply hope that the attack will end and that they will be spared. The more sensible people would quickly run to the wilderness and hole up in structures that are not visible from the air.
The aliens then identify various human military bases on Earth and conduct tactical orbital strikes at closer orbits. The entire US Navy fleet is completely destroyed, and so are other navies around the world. All US bases (that are visible from the air) are also completely destroyed, and so are the bases of all other nations. The aliens would have estimated the amount of firepower needed via their fake asteroids sometime ago. Other locations targeted will include palaces, observatories, power stations, farmlands, etc. The aliens would also bomb population centers with chemical weapon strikes. Again, the less technologically advanced a particular country is, the less affected it is. Eventually more secret US military installations are discovered via signals intelligence and bombed with penetrator rounds from orbit.
The aliens then send fighter craft. Many millions of them, of which most are robotic. The US attempted to shoot down some of the craft with stealth planes launched from underground hangars, but the aliens also have some stealth aircraft, multi-spectrum radars and really powerful air-breathing ion engines, and thus quickly overwhelm the venerable F-22s and destroy those hangars.
At this point, utter devastation. London, once the capital of the most powerful empire on Earth, was bombed to oblivion with chemical weapons. This time, the Brits did not have gas masks as the aliens attacked very quickly. Just like the Americans, the Russians suffered very heavy losses. Far more devastation than Nazi Germany would have imagined when starting Operation Barbarossa. With the Israelis, the number of deaths in Israel make the Holocaust look like a small pogrom. The Kaaba was bombed for obvious reasons. Many millions of targets to kill off easily. Also the Vatican too. What about Africa? Well, relatively less damage due to lesser population density, and there would have been more survivors roaming the wilderness because its much bigger in Africa. Shanghai was reduced from the world's biggest city to a desolate, toxic wasteland. Melbourne is the most liveable city no more. The Statue of Liberty was knocked over by debris from Manhattan being obliterated. Rio De Janeiro was unfortunate to suffer both orbital strikes and later megatsunamis caused by orbital bombardment in the oceans.
At this stage, the aliens begin landing on the ground en-masse, forcing human survivors to retreat.
Ironically, more Africans survived than any other racial group simply because of their lack of military developments, but they are no more likely to survive than any other groups of humans remaining on Earth.
After studying human history, the aliens would laugh at various human racial supremacist groups, as there was no difference between any human ethnic groups. Perhaps the aliens were right in wiping out the humans, given that the aliens have seen enough death and destruction on their home planet in another arm of the Milky Way galaxy. Back to hunter-gatherer lifestyles for humans, of which most are Africans by now and probably some South American counterparts.