This section is on infinitive constructions.
διὰ τὸ τοὺς πολεμίους ἐν τῇ χώρᾳ μένειν φεύγουσιν οἱ πολῖται.
My incorrect answer (twice): On account of the enemy in the country, the citizens are fleeing to wait.
Answer key: Because of the fact that the enemy are remaining in the country the citizens are fleeing.
I think "διὰ τὸ τοὺς πολεμίους ἐν τῇ χώρᾳ" is all linked together; the preposition διὰ + acc., which includes both ...