Early in the first half of the 11th century nearly the entire area was under the rule of the Emperor in Constantinople (save areas under Slovene dominance and Dalmatia). The lands of modern Romania however were eaither under the rule of The Magyars or some other Western Steppe nomads.

By the end of the 11th. century, the Serbs had won a large amount of independence, near the end of the 11 hundreds the Bulgarians had also reaserted their independence. The area seemed to have some semblence of order.
In 1204 however, the Latins Conquered Constantinople and the region spirraled into fragmentation. Greece was subjected to the whim of many minor Crusader Kprincipalities, the Despotate of Epirus and the Empire of Nicea. The Serbs held a small state and the Albanians had independence, thugh a short one. By the 1350's the Magyars/Hungary had extended it's rule over Carpathia and the rest of modern day Romania. Bulgarian holding had been severley chipped away, Serbia controlled lands form the Danube to the Gulf of Corinth, the Italian Republics such as the states of Venice and Genoa grappled for the Greeks islands, the Crusaders held southern Greece and Byzantium was nothing more than a collection of isolated provinces.

The Byzantines had always been the dominant cultural and even political entity of the Balkans but increasingly the Latins had a hand in millitary matters. The Latins mostly affected Bosnia and Croatia and in a lesser way, Serbia. Technology from the Latins came through Hungaria. Ragusa also served as major route for the importation of Istalian arms and armour.
Slowly the Elites of the Western Balkans became more Latinised but those of the eastern Balkans were less dramatically changed. This is due to their closer relations to Constantinople.
They were also more exposed to Turkic nomadic cultures as well.

The millitary culture of the Bulgarian Empire (late 12th to 14th cen.) is based upon the 12th century Comnenid Army, this was when they were also subjects of the Comnenids and served in their armies. Russian arms are also found in the Bulgarian Empire, probably through trading links with Byzantium and the mutual threat of Steppe Nomads. Although HA was relegated a minor role and left to allies. This seems to be the same as in 11th century Makedon.

Serbian millitary culture seems to be in the Western tradition.
Spears, maces and Latin straight swords for Horsemen and the elite, spears staff weapos, bows and later xbows for the infantry. The millitary was the classic Latin Feudal one, made up of local lords and mercenaries, local and foriegn. The latter were in most cases Germans, but by the mid 1300's Catalans and men from the Latin Spanish kingdoms dominated.
The Serbian army was structured in battles of 15, 50, 100, 1000. It's stregnth was cavalry and foot archery. The armed levy of peasents was rarely called up however.
The 14th century saw two major developments, either via the influence of Hungary or the Turks, the adoption of curved sabres and comppsite bows.