the war has now begun vs the war has begin

please,could someone help me to know and understand and as well when to use both phrases “The war has now begin
and the war has now begun.But the emphasize is on the” begin" and “begun”.thanks

You’ve written the same phrase twice. ‘Begin’ would not be used correctly in that phrase.

But Mr.beeeseees If you insist that ‘begun’ is correct i dont really understand why past participle should be used with the present “has”.As in the war has now begun.thanks

Your argument about the verb tenses seems confused.

The war has now begun - is correct.
The war has now begin - is incorrect.

The war now begins - is correct.