Original: Allied with China under the Tang dynasty , Silla conquered Goguryeo in 668 , after having already conquered Gaya in 562 and Baekje in 660 , thus ushering in the North-South states period with Later Silla to the south and Balhae to the north .
Simplified: The time of the three kingdoms ended in 668 when Silla conquered the other two . It beat Goguryeo after Baekje .