Simplify the following text for a Grade 9 native English-speaking person.
Original: In late 1940 he was again arrested in Zagreb because of a congratulatory telegraph to Jozef Tiso , president of the newly formed Slovak Republic ( 1939 â `` 1945 ) , signed by a number of Croat nationalists .
Simplified: In late 1940 he was arrested in Zagreb due to a congratulatory telegraph to Dr. Jozef Tiso , president of the newly formed Slovak Republic , signed by a number of Croat nationalists .