Simplify the following text for a Grade 7 native English-speaking person.
Original: The battle started when Minamoto no Yukiie attempted a sneak attack against his enemies during the night . He found Taira no Tomomori and his army directly opposite from his , along the Sunomata River , near the borders of Owari and Mino provinces .
Simplified: Minamoto no Yukiie and his army found Taira no Tomomori 's army across the river .