In the past, during the Ottoman empire, a lot of Muslims were killed be non-believers who were defending their homes. You know, people from countries like former Yugoslavia, Hungary, Slovakia etc. killed a lot of dedicated Muslims, because they were defending their land from the occupation by Ottoman forces. What did happen to those Muslims? Will they experience Jannah?
Firstly, no one can decide who will go to heaven or hell. At judgement day, Allah is going to give final decision based upon our actions.
In this world, we can only express our views like "this is good or bad" according to our observations on events.
There are different perspectives on those events which you refer. One of them is "Ottoman did these wars because of "Jihad". So, their actions were justified."
You can bring some evidences to prove this idea is wrong, or they can show some evidences that explain their findings are true.
In my opinion(Allah knows the best), saying like "the person will go to heaven or hell" is not good and this is not our business.
We can say this behavior is wrong and doing this is a sin based upon rules of Quran and guidance of Hadiths.
Any muslim who was martyrd fighting for islam against the kuffar/ non believers will go to Jannah (paradise).
And whoever desires the Hereafter and strives for it as he ought to strive and he is a believer; (as for) these, their striving shall surely be accepted." [17:19]
The only issue how Allah will decide to reward them, did they die in a noble way? how many non-believers did they kill or convert before their martyrdom? Did they give their life willingly for Allah and did they die with their eyes open?
Serving [the believers] will be Houri (immortal youths with beautiful of eyes and well rounded breasts) with jeweled and crystal cups filled with the purest wine which will neither give them headache nor hangover, with fruits and meats of their desire. They will be fair ones with lovely intense eyes like guarded pearls; A reward for the good deeds of their past life. [56:17-24]