Coudn't you defeat aliens with just guns?
Kill an alien with a gun? Sure, for human-sized aliens made of meat anyway. Meat is meat, and guns were designed to drill holes in it.
Defeat that alien's technology with guns? Unlikely, because we can't even defeat human military technology with guns.
If aliens invade, it won't start with foot soldiers any more than a US military invasion starts that way. It starts with you being introduced to their equivalent of a Tomahawk missile loaded with cluster bombs. Next comes the artillery barrage to soften up any resistance, followed by their equivalents of attack helicopters and tanks. The best you can probably do is hide in a hole hoping one of the bug-eyed monsters opens his hatch to get some fresh air while in rifle range, because if you move you're dead.
Except, since it's advanced aliens instead of the US Army, it'd actually be much, much worse. Maybe they spray the atmosphere from orbit with a custom virus that kills off 99.9% of humans. Or they can divert asteroid after asteroid as a series of city-killing impacts, until we surrender. That'll be popular since there's absolutely no risk to the attacker. Limited to chemical rockets, we'd have no short-term way to retaliate against an enemy sitting in the asteroid belt throwing rocks at us.
No, guns alone won't be much use against viruses, asteroids, or nanobots that disassemble all matter into "gray goo"... Any more than they are against today's heavy weapons.
well this is a hard question to answer as we haven't actually seen any aliens. So we don't know how technologically advanced they will be, but as chances are THEY will be visiting us they are most likely going to be far superior to us tech wise. I doubt that if a species advanced enough to travel space and come to this planet would be easy to beat in war. Chances are they will have superior weapons and body armor.
They could develop shields like in the halo games or they could have body armor that is tough enough to easily stop a bullet. They could be so advanced it would be like trying to fight a tank with bow and arrows.
But as we may never really see alien life in our lifetime you will probably never get a solid answer to this question.
The Iraqi army got stomped by the US army hard in Gulf War 1.
The technological differences were minor compared to anything an alien race can bring. Add in the fact that they could also use space bombardment, robot infantry and vehicles, you might never even see an alien.
No alien losses...Easily replaced machinery and robots that simply need no life support to move between stars. They could also build robotic factories on Mars, mine it automatically and keep feeding robots at us till they finally crush us.
All while losing zero alien losses to us.
In fact the only real fatalities that might occur, is when the alien on the mother-ship slips in the Kitchen, while making himself a sandwich during his lunch break.
Depends on what aliens you are encountering.
If the aliens look like this :