Need a book recommendation.

[Danyaal]

Hey Guys, I just started reading light novels and one i found particularly interesting was Gate.(http://myanimelist.net/manga/67879/Ga...)
I have been trying to find LN or any media that is similar to the premise in this story where modern troops square off against past or outdated soldiers. Any recommendation is welcome.

[Aaron]

I have seen this called military portal fantasy before, it used to be more popular but now it's a bit more sparse.

A Long Time Until Now *literally what you are asking for.

Into the Storm *same but this time navy.

1632 *This series is very up and down in quality...the 1634 books (except Baltic Fleet which was great are probably the worst)

Off Armageddon Reef *Not portal fantasy but using modern tech vs old society. This is also probably the strongest series of the bunch, though the series suffers a bit from a seeming lack of editors.

Log Horizon, Vol. 1 *I feel it almost counts because of the way they approach the being stuck in MMO world. But it's mostly because of the strong overlap in people who like this compared to people who like the above.