Why did they do this?

Why did the terrorists of the middle east attack and destroy the World Trade Center? What were their motives?Who first came up to the plan and when?Why choose this year and the day?What was the other incident in 1993?Why did they choose this building?Were they relly aiming for the White House when they crashed into the Pentagon?Was the last plane heading for the Capitol?How many people were killed?Why would they build a building on the WTC memorial site?Any links to videos?Only serious answers.Thanks.