Western European languages tend to have fewer genders and simpler case systems than Eastern European ones, is this due to contact?

Question

You can draw a relatively consistent line through Europe, to the west of which, Indo-European languages mostly have one or two genders and nouns don't inflect for case, and to the east of which, languages tend to have three genders and nouns do inflect for case. Roughly speaking, this would run east of Sweden, through the Baltic sea, along Germany's border past Denmark, the Netherlands, French/Italian speaking Switzerland, to the Italian-Slovenian border, and finally through the Adriatic sea.

The one modern Romance language I'm aware of to have preserved three genders and nouns that inflect for case is Romanian - to the east of this line. The Slavic branches retain three genders and nouns are inflected for case, along with Greek and Albanian. To the west of the line, the Celtic languages have two genders ~and nouns don't inflect for case~ (EDIT: they do). Many Germanic languages have a common-neuter gender distinction, or no gender at all as with English, and minimal case markings.

There are exceptions here: Icelandic, Norwegian, some dialects of Danish and formal Dutch preserve three genders (but don't inflect nouns for case). Conversely, the Baltic languages classify their nouns into two genders but inflect by case. You could also argue my question is a bit stilted because my "east-west" line circumnavigates Germany! (Maybe timezones give me a precedent for this misbehaviour!)

Another answer notes that "Questions of the form "Why?" in historical linguistics are not necessarily answerable, but we can try." So – I'm afraid I'd like to hear your thoughts on how this east-west distinction has come about!

More specifically, is it more plausible that

a. there's a sprachbund effect among languages in the various IE branches west of this line? (I'm aware of Standard Average European, but I'm talking about features local to "western" Europe, as per my definition above)

b. this is just random chance?

Answer 1

Except for linguistic islets such as Basque, Finno-Ugric languages or Turkic languages, modern Europe is dominated by Indo-European languages, so the question should be easy to answer. If we restrict ourselves to Indo-European languages, we have three branches in Western Europe: Romance, Germanic and Celtic languages, while Eastern Europe is somewhat more diverse, Baltic languages, Slavic languages, Albanian, Balcorromance and Greek (in the past the situation was more complex, but today it is simpler).

The Romance languages confused the neuter and the masculine by a phonetic erosion of the desinences, which were already similar. A similar situation occurs in West Germanic and Nordic, where the declension of masculine and neuter was similar. There is evidence that in both branches the merging of masculine and neuter began to occur before the contact was intense. This is also the case in Celtic, although the masculine-neuter confusion began earlier in the Brythonic languages than in the Goidelic languages.

The Slavic and Baltic languages did solidly maintain the tripartite gender (masculine, feminine, neuter), even though in many places they had contact with genderless languages such as the Uralic languages. Romanian had a notorious contact with Slavic languages, but still did not lose the neuter gender. So it seems that the main cause of the loss of the neuter in Western Europe was contact.

For these reasons, I would say that the confusion between masculine and neuter in Western Europe may have been due to internal causes (in the case of English, indeed, contact with Scandinavian languages seems to have influenced the total loss of gender in nouns and adjectives, although not in pronouns).