Simplify the following text for a Grade 7 native English-speaking person.
Original: The interwar period ( 1918 â `` 1939 ) is understood within Western culture to be the period between the end of the First World War and the beginning of the Second World War .
Simplified: The interwar period was a time in history between the two world wars , World War I and World War II , which was between 1918 â `` 1939 .