How did the multi-ethnic cultures of Balkan led to the country's demise?

The multi-ethnic cultures of the Balkans led to severe conflicts between polarized groups, culminating in wars in 1912 and 1913. Since then, the division of any country into small, hostile units has been known as "Balkanization." The primary reason this led to the destruction of the original country was the impractical division of power. The new political units were too small to effectively unify the region, destabilizing its populace and throwing off the balance of power. The balance between governmental authority and population is a delicate one, and the fact that there was no central government across the region led to irreversible damage.
In addition to the fractured government of the Balkans, the cultural divide became too great to overcome. What was once a relatively cohesive culture was fractured into many smaller parts, creating an environment of harshly competing values. This competition led to various conflicts throughout the region and destroyed any existing sense of cohesion. While many multi-ethnic societies around the world thrive through peaceful coexistence, the political tensions between ethnic groups in the Balkans were too severe to overcome. Due to the vast expanse of the Ottoman empire and the diversity of the members of the Balkan League, those differences resulted in total structural collapse.
It is worth noting that in most multi-ethnic countries, the individual groups have shared geographic proximity for far longer than the groups in the Balkan League. Each of these factors contributed heavily to the Balkan Wars and the collapse of the Ottoman Empire in Europe.
https://www.britannica.com/topic/Balkan-Wars