Simplify the following text for a Grade 9 native English-speaking person.
Original: On August 7 , 1942 , Allied forces , predominantly American , landed on the islands of Guadalcanal , Tulagi , and Florida in the southern Solomon Islands with the objective of denying their use by the Japanese to threaten the supply and communication routes between the U.S. , Australia , and New Zealand .
Simplified: On August 7 , 1942 , Allied forces , mainly from the United States , started landings on the islands of Guadalcanal , Tulagi , and Florida in the southern Solomons with the aim to make supply routes between the U.S. , Australia , and New Zealand safer .