Here is a pattern sentence asking a question: "Where did you get that book?" Another sentence goes: "What made you decide to leave Russia?"
Why not to use "What did make you decide to leave Russia?" as in the first example?
I don't understand the following: both sentences have past tense but only one uses "did" to make the interrogative sentence. Why is did omitted? Perhaps it's just the way it is...
In open interrogatives, the inversion only occurs when the wh-word is not the subject. This is why the inversion occurs in the first sentence because where corresponds to adjunct in the answer to the question.
Where did you get that book? --> I get it from the library.
Inversion does not occur in the second sentence because the wh-word is the subject.
What made you decide to leave Russia-->The war made me decide to leave Russia.
Note, you can use "did" there, but in that case it acts as an intensifier.
You say you didn't leave because of the political situation. So, what did make you decide to leave Russia?
