John Trapp on Nahum 1:8

Ver. 8. But with an over-running flood he will make an end of the place thereof] i. e. of Niniveh that great but bloody city chap. 3.1. Her ſtate ſhall be utterly ruinated as the old world, by the generall deluge. But becauſe the word here rendred flood is uſed of rivers that overflow the bankes 2 Chron. 32.4. and the adjunct over-running alſo implies as much (See Eſai 8.8. Dan. 11.10, 40.) I ſuppoſe the Holy Ghoſt here forethreateneth that ruine of this city by the river Tigris, which at an inundation broke out upon the wall, and threw down twenty furlongs thereof. This was a ſad foretoken to them of their enſuing deſolation by the enemy (as that raine was that fell in Egypt) where it uſed not to raine (a little before Cambyſes with his Perſians ſubdued it) for it fell out in the time of the Siege, as Diodorus teſtifieth, according to an oracle that the Ninivites had received by tradition from their progenitours, ſc. that their city ſhould then be taken by the enemy,Diod. Sic. when the river took part againſt them: and it fell out accordingly.

and darkneſſe ſhall purſue his enemies] i. e. terrible and inextricable calamities ſhall overtake them: their ruine ſhall be irreparable. And indeed it may now be ſaid of Niniveh, which once was of a great city in Strabo, Magna civitas, magna ſolitudo See Zeph. 2.13, 14, 15. Druſius rendreth it thus, Hoſtes ſuos perſequi faciet tenebras, He ſhall cauſe darkneſſe to purſue his enemies, Or, He ſhall make his enemies to purſue darkneſſe, according to that noted ſaying of the Ancients, Deus quem deſtruit, dementat, whom God intends to deſtroy, him He firſt infatuateth. But the former ſence is the better.