Why did Pentagon attack The World Trade Center?
Unless you REALLY like far-fetched Conspiracy theories, Pentagon DIDN'T attack the WTC. Terrorists of a supposedly Muslim inclination attacked BOTH Pentagon and the WTC.
Pentagon b/c it's a symbol for American Military, WTC b/c it represents a reasonably open World where goods, ideas and people are free to move.
Both of the above being things the planners and funders of the attack didn't like.