Were Serbs and Croats one people / tribe in the past? If not, why do they speak the same language?

Question

Were Croats and Serbs one people that were later (politically) divided, or two unrelated peoples that came in the same area and (linguistically) merged?

Before, I thought that Serbs and Croats were, in the near past, one people of which some adopted Catholic religion (now called Croats) and some Orthodox (now called Serbs). I still think that this is the case of Serbs and Bosnians: Bosnians are Serbs converted into Islam under Turkish rule, so no wonder they speak (almost) the same language. Hindi and Urdu is another example of such division.

The more I read, the more I feel Serbs and Croats are unrelated Slavic tribes which came to Balkans separately and never had shared history or culture. Not one people divided, but rather two unrelated peoples culturally and linguistically merged, as they happened to settle next to each other. Is this true?

And if they don't share (recent) common ancestry, how come they speak (nearly) the same language? I guess their unrelated ancestors spoke different (Slavic) languages. Have Croats adopted the Serbian language? Or vice versa?

I don't mean 19th century agreements of unification of the Serb-Croatian language, I mean why did they speak such similar languages in the first place long before the 19th century?

Answer 1

According to the entry concerning the Southern Slavs it is quite probable that the common language source would be due to common ancestry:

The Byzantines broadly grouped the numerous Slav tribes into two groups: the Sclaveni and Antes.[8] They are both first encountered in the lower Danube region. Some, such as Bulgarian scholar Vasil Zlatarski, suggest that the first group settled the western Balkans, becoming one of the forerunners of the linguistic group that became the Bosnians, Serbs and Croats,[9] whilst offshoots of the Antes settled the eastern regions (roughly speaking), becoming one of the ancestors of the Bulgarians.[8][10]

So at this time (the 6th century),they were considered to be a single group by the Byzantines.

At some later point, they are referred to, again by the Byzantines, as two separate peoples:

Constantine VII in De Administrando Imperio recounts in 30th chapter "ancient Croatia, also called "white", is still unbaptized to this day, as are also its neighboring Serbs... plundered by the Franks and Turks and Pechenegs..."

(emphasis mine) from entry on White Croatia

So there is a basic line of thought which would place both the Croats and Serbs as a common people with a common linguistic root, considered by the Romans as a single group the Sclaveni, but which hundreds of years later were reffered to as two distinct groups by Constantine VII( reigning from 913 to 959).

Answer 2

The Serbs and Croatians, were and are part of the larger South Slavic ethno-linguistic and ethno-racial group. What primarily distinguished Serbs from Croatians-(or Croatians from Serbs), was religion, namely, a sectarian difference.

Both Serbs and Croatians have been Christians since the Middle Ages, though the Serbs have been and are still, Eastern Orthodox-(or of the Byzantine rite), whereas Croatians have been and are still, Roman Catholic-(or of the Roman rite). Serbia and Croatia are South Slavic Balkan lands, though they have different historical identities.

The Serbs lived under Greco-Byzantine Christian rule for centuries (and, for a short while, the Serbs founded their own independent state during the Late Middle Ages, though remained steadfastly loyal to Eastern Orthodox Christianity). However, the Croatians had peripheral contact with the Greco-Byzantine Empire-(comparatively speaking) and early on in their history, became increasingly associated with-(as well as conquered by), The Roman Catholic Venetians. The Serbs were conquered by the Ottoman Turkish Muslim Empire for much of the Modern era, though the Croatians were conquered by-(or were a quasi-tributary state under), Venice for centuries-(and unlike the Serbs, the Croatians, with the help of the Venice, defeated the Ottoman Muslim imperial onslaught). The Serbian Christians have had a more Eastern cultural and religious orientation, whereas the Croatian Christians have had a more Western cultural and religious orientation. Yet, both Serbs and Croatians, are fellow Christians

So, as you can see, the sectarian identities of both Serbian and Croatian Christians was very much formed under the historical circumstances surrounding each country.

Answer 3

Currently, Croatian scientists declared that studies show that the Serbian genetics, though very similar, but not identical, to that of Croatians, is older than that of Croatians to the point that Serbs may have fathered the Croatian nation. (I had both a Croatian grandmother and a Dalmatian grandfather. The Venetians came into the Zagora hinterland and helped drive back the Ottomans and then remained, tore down all but one minaret, and helped transition the residents from speaking Old Dalmatian to Veneto. That remained the case even 1 1/4 centuries later when Napolean conquered the Venetian republic but changed when the first Yugoslavian king, a Serb, forbade any Latin language to be spoken. Distant Dalmatian cousins of mine there to this time communicate only in Croatian and consider themselves Croatian citizens. My father in the USA preferred to speak Veneto, otherwise Triestin, I speak English, and my mother spoke Spanish. Languages can change but genetics don't.)