The Baltic anguage family forms a major branch of the Indo-European languages. The Indo-European family includes many of the most widely spoken languages in Europe and parts of Asia. For an accessible introduction to this larger language group, see:
The Indo-European Language Family – Overview: https://englishmadessimple.org/the-indo-european-language-family/

The Balto-Slavic language family forms a major branch of the Indo-European (IE) language phylum. It encompasses the Baltic and Slavic languages, spoken today across Eastern and Northern Europe. Although the precise historical relationships between the Baltic and Slavic branches remain debated, comparative linguistics, phonological innovations, and shared morphological features strongly support the idea of a common proto-language, known as Proto-Balto-Slavic, which is believed to have diverged from Proto-Indo-European (PIE) during the late 3rd to early 2nd millennium BCE.

Position within the Indo-European Family

For a dedicated introduction to the Slavic languages, their history, and regional development, see:
The Slavic Language Family – An Overview: https://englishmadessimple.org/the-slavic-language-family-an-overview/

Historical Background

Proto-Indo-European Roots

Linguists generally agree that the ancestor of the Balto-Slavic languages, Proto-Indo-European (PIE), was spoken around 4500–2500 BCE, most likely in the Pontic-Caspian steppe region. As communities expanded, PIE diversified into separate branches.

Formation of Proto-Balto-Slavic

Proto-Balto-Slavic likely formed as a distinct speech community around 2000–1500 BCE, situated in the forest-steppe zone of present-day Belarus, Lithuania, northern Ukraine and western Russia.

Evidence for Balto-Slavic Unity

This strongly suggests a common ancestral language, rather than parallel evolution.

Divergence into Baltic and Slavic

The split between Baltic and Slavic is estimated to have occurred around 1500–1000 BCE. However, archaeological and linguistic data indicate that long-term contact continued, allowing mutual influence.

The later rapid spread of Slavic began around the 5th century CE, while the Baltic languages remained concentrated around the eastern coast of the Baltic Sea.

The Baltic Language Family

The Baltic languages are known for their conservatism — they preserve vocabulary, grammar, and even tonal accent patterns remarkably close to the early Indo-European model.

Classification of Baltic Languages

Lithuanian and Latvian: Divergence and Development

Although both are East Baltic, Lithuanian and Latvian began diverging between the 5th and 7th centuries CE. The divergence was shaped by different external contacts:

Comparative Features: Lithuanian vs Latvian

The Slavic Language Family

The Slavic languages later expanded dramatically. For a detailed overview, history, and maps, see:
https://englishmadessimple.org/the-slavic-language-family-an-overview/

Slavic languages are characterised by aspectual verb systems, palatalisation of consonants, and historically a Church Slavonic literary tradition.

Comparison: Baltic vs Slavic

TIMELINE DIAGRAM

Conclusion

The Balto-Slavic language family is central to understanding the linguistic and cultural history of Eastern Europe. The Baltic languages preserve some of the oldest Indo-European grammatical structures, while the Slavic languages evolved into one of the most widespread and culturally influential linguistic groups in Europe. Their shared origins demonstrate the deep historical connections between the peoples of the Baltic Sea, the East European Plain, and the Balkan Peninsula.