[HISTORICAL ISSUE] - South Slavs and Avars…

[Son of Fire]

A question has been nagging in my mind today after getting some information pertaining to the South Slavs… that being, that the South Slavs, Serbian, Croatian, and other tribes fought and crushed the Avars to fully settle in the Dalmatian region.

Now, from what I have seen in literature and such has stated that the Slavs generally didn’t have much in the way of cavalry, armour, or even weapons… not to say they were destitute, but they just didn’t have access to the kind of military kit that other cultures did (mainly shields, spears, javelins and axes, not quite comparable to the available kit of other cultures).
While the Avars were a fairly effective militaristic steppe culture, with ample horses, swords, bows, lances, and armour… who has been fairly effective military force in the region for some time.

It seems to me a bit perplexing then how the Slavs managed to break them in Dalmatia.
I mean… how did they manage it?
With the preconceptions that I have and that I just mentioned, it doesn’t make sense.
The only things I can think of are…

Overwhelmingly outnumbered… but that seems a bit dubious.
A very large Byzantine military contribution… possible.
Or, that perhaps the South Slavs were not as limited in their military kit, and tactics as we once though… perhaps possible.

Thoughts?