For example, Albania and Bosnia are two countries with a muslim majority, while their neighbors: Greece, Serbia, Croatia etc.. Are predominantly Orthodox or Catholic.
Also, did the Ottomans convert people using force? Or simply through taxes? (Muslims payed fewer taxes).
This question has been asked before, and I think they have done a fantastic job at answering.
/u/UrbisPreturbis gives a very detailed explanation here. Continue reading the thread as a whole. I can summarize it by saying, there is a significant Muslim minority now in other Balkan countries, and many Muslim were expelled or re-converted in the past, but that wouldn't do his answer justice. It's worth the read, it's the most detailed answer out of all these I'm providing.
This answer is on Albania only, but tackles something different, the right to bear arms. Non-Muslims were not allowed to bear arms, and this was an important aspect of Albanian culture before the Ottomans.
There was an AMA on Modern Islam and this question was asked again here
This was mentioned by /u/UrbisPreturbis, but here is an answer of why didn't Greece became Muslim. From the top comment:
"Most Greek-speaking Muslims in Greece left for Turkey during the 1920s population exchanges under the Convention Concerning the Exchange of Greek and Turkish Populations (sometimes in return for Turkish-speaking Christians such as the Karamanlides), with the exception of the Muslims in Thrace, who are officially recognized as a minority."
/u/el_gringo_exotico also offers an answer on the political environment in Bosnia that let part of the population to embrace Islam, here. Bosnian population tried to differentiate itself from the population of Austro-Hungaria, starting a Bogomilist influenced church first, and then conversion to Islam, a phenomenon also observed with Albanians and Bektashim (see below)
Does muslim majority mean that more than 50% of the population is muslim? Can you provide a source for Bosnia & Herzegovina? I was under the impression that christians outnumber muslims in B&H.