Nowadays it is not yet evident whether Germanic used to be a part of Germano-Balto-Slavic community or it was closely connected with other Indo-Euroepan language groups. Many linguists fairly find Germanic parallelisms in Armenian (mostly in phonetics), Greek, Italo-Celtic, Tocharian languages. It is a so-called "centum" language, for Indo-European *k turned into Germanic k, while in Balto-Slavic it appeares as s or [sh], so they are considered "satem" languages. But still much evidence is found about Germanic close relation with Baltic and Slavic groups, both in morphology and vocabulary.
Germanic tribes came to Europe, as we may suppose, from Asia through lands along the Volga, then via Eastern Europe, and settled in the north of Europe, colonizing also Scandinavia. In the beginning of the AD era, they began fast and wide migrations to the south and west, pressing toughly Celtic, Slavic and other European tribes living here. But though different Germanic nations occupied in the 4th - 8th centuries practically all Europe: lands of modern Italy, Spain, France, Germany, Low Countries, Ukraine and Crimea, founded their kingdoms in Sicily and in Northern Africa, - but they were easily assimilated by substratum peoples or by future invaders, and now occupy about a third of all territories conquered by them in the early Middle Ages.
The Germanic language, before it was divided into several branch tongues, had some bright characteristic features. The Ablaut, vowel interchange in the stem, was used here much more widely and functionally then in Proto-Indo-European. The stress, free in Indo-European, was fixed on the first syllable in Germanic. The opposition of aspects which dintinguished the Indo-European or Balto-Slavic verb, was changed with the opposition of genders, which were three: masculine, feminine, neuter. Verbs used in Germanic were either strong or weak, and the second formed their past tense with -t- / -d- suffixes, derived from Indo-European *-to-. The noun had supposedly four cases, though in some dialects instrumental (West) and vocative (East) were still used. The verb had a complex system of tenses, including infect (imperfect) and perfect differences.
Germanic vocabulary is quite and quite Indo-European. Only about 30%
of words are not found in any other Indo-European groups. Germanic words
have cognates in Baltic, Slavic, Italic, Celtic, Venetic,
Illyrian, Indic languages, and it is impossible
to detect the closest language by these numerous cognates.