I supposed your friends are still young? How old are they? 20? 22? What your interest in is for your own liking. Do not be concerned with their comments that makes you upset because they do not seem to find something better to say like, "Who da current champ of rock climbing?" or "Whats da latest military model dat you tink can be implemented in SG?"
Of course you cannot say their interests are stupid too. DOTA, Maple, club, girls, etc, etc. Its the current "in" thing many people are following. I have friends who play DOTA and I kinda like it, I do not like Maple even though it is cute, the people you face online tends to make you angry easily and too addicted to it has a "less than" nice effect on the person playing. Clubbing, girls, etc, etc are simply more general stuffs for guys and girls. They can communicate well due to a common topic or interest.
I like ancient history and military equipments (to a certain extent). I know abit about Roman era and much on China history (especially the 3 kingdoms period) and I know a fair amount of some weapons and specifications (Is P90 the more prefered weapon for special ops or smth in US? I noe dis 1 go ask in Military nuts or other Military related forum), I like video games and more common things like "bio" girls (

) and etc, etc.
From what you have typed, I see you have mingled with this particular group of friends quite alot. If you still have some issues, you can either tell them about it OR you mingle with them less and with some other people who appreciate your interests more.
No one can stop you from loving what kind of interests you like. Its in your onus to make sure you do not get affected by their remarks too negatively. You can simply treat it as "I am different, no big deal" and smile back.
