Answer 1

Assuming you are talking of the movie, the answer lies in the prior movie, The Rise of Darkrai. The battle between Dialga and Palkia in that movie caused massive damege to the Reverse World, enraging Giratina. Wanting revenge, Giratina tried to kill Dialga.
Source: http://bulbapedia.bulbagarden.net/wiki/Giratina_(Pok%C3%A9mon)#Major_appearances
Source: http://bulbapedia.bulbagarden.net/wiki/Dialga_(movie)#History

Comments

its distortion world

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no, it is reverse

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http://bulbapedia.bulbagarden.net/wiki/Reverse_World
http://bulbapedia.bulbagarden.net/wiki/Distorted_World
Actually, you are both right, the "opposite world" is called
 the Reverse world in the film and the Distortion Workd in the game.

Answer 2

it is because in the movie that palkia and dialga battle the distortion world became with alot of toxic clouds, so giratina wanted revenge with palkia and dialga.
source: I watched both movies

Comments

the  movies were giratina and the celestial warrior and the rise of darkrai

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not celsetial, SKY warrior

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thanks is because i speak spanish and it was "guerrero celestial" english: celestial warrior

Answer 3

No, Giratina doesn't want to. It is possible that he does what to because he wants space EVERYWHERE.

Comments

how ? in the movie, giratina wants to destroy dialga

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Lucario, no one really knows the answer, don't give anyone a BA, this is a theory question, you would have to talk to the writer  of that movie to find out

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There is an answer.....>.<

Answer 4

No one really knows, it's the way game freak wanted it, also Giratina was also banished for his violence, and he's being violent so, that could be another thing. In the end no one really knows the answer to that question, also doesn't that make it entertaining.