Where did the dative ending go?
Whenever I read some text from like 80 years ago they always write for example "nach dem Kriege" instead of "nach dem Krieg".. did that "E" disappear because people got lazy or was it just not needed or what? If so, how come nobody ever says like "Vorsicht bei dem Abfahrt des Zug"? It's not needed there either because I know what case it is thanks to "des".
I don't know why the E was dropped, in much of Schubert's great Lieder you see the additional E with the dative very often. Likewise many th's where the H has now been lost. (Thräne > Träner etc)
This is also a good example that the e is not only dropped in the dative: both Zuges and Zugs are valid Genitiv forms of Zug.
This is a great example of how languages change over time. I don't know if I would characterize the dropping of the dative 'e' as laziness, but it is certainly something that started in casual usage, then became widespread enough that it became proper grammar. If you used it today you would sound very old-fashioned. You still find the dative 'e' in written German in the early twentieth century.
Interestingly, there are a couple of set phrases where the dative 'e' is still used:
'zum Tode verurteilt' (sentenced to death)
Let's not forget "Und als ich die deutsche Sprache vernahm, / Da ward mir seltsam zuMUTE;/Ich meinte nicht anders, als ob das Herz/Recht angenehm verblute"
Beim Barte des Propheten, darüber hab ich noch nie nachgedacht. Im Zuge dessen werde ich darüber Nachforschungen anstreben. In diesem Sinne: Schönen Abend !
Vorsicht bei der Abfahrt implies something else "fährt ab" (like a train) and Vorsicht beim Abfahren implies to me that you "fährst ab" like if your skiing teacher tells you "Vorsicht beim abfahren, die Route ist wirklich gefährlich". At least that is whats happening in my mind.
As an added note, I'm pretty sure that the dative ending was one of the many German grammar points that Mark Twain complained about in one of his essays. Among the several suggestions that he made in order to "improve" the German language, he suggested that the whole entire dative case should be thrown out.