Formal writing: clauses into nouns
Formal writing often replaces a clause with a noun phrase. Nach plus dative can replace after; wegen plus genitive expresses a reason in standard formal German. The preposition determines the case of the noun phrase.
Understand the idea
Formal German often expresses relationships through noun phrases rather than full clauses. A time or cause clause can become a prepositional phrase. This changes grammar as well as style: the new preposition governs a case, and the noun phrase needs appropriate endings.
Build it step by step
Identify the relationship first, such as time after an event or the cause of a result. Choose a suitable noun and preposition, then apply the required case. Nach takes dative; formal wegen typically takes genitive. Longer noun phrases can include adjectives and possessive relationships, so check the whole phrase rather than a single article.
See it in a sentence
Nach der Sitzung gehen wir nach Hause.
Nach dem Essen machen wir eine Pause.
A useful memory aid
Convert one short clause into a noun phrase and back again. Keep the meaning stable while noticing what happens to the finite verb and the case endings.
A common trap
Do not leave a finite clause after a preposition that requires a noun phrase. Also avoid making a sentence harder to read merely to sound more formal.