Simplify the following text for a Grade 8 native English-speaking person.
Original: During the Second World War , Romania tried again to remain neutral , but on 28 June 1940 , it received a Soviet ultimatum with an implied threat of invasion in the event of non-compliance .
Simplified: In World War II , Romania called itself neutral . However , on June 28 , 1940 , a Soviet ultimatum said that they would invade Romania if they did not join the Axis Powers .