First thing first it wasn't developed in Bulgaria it was developed in Solun Cyril and Metodije where from Solun and they where going on a mission from Romans to Slavs in Moravia.
Second Cyrillic alphabet has emerge from greek alphabet and third they gave as land to settle there was no major battles
force your argumets whit more facts it is the only way to study history but some facts that you have are a somewhat uncorrect but never mind that is the thrill of History we make mistakes we read and we correct them