[SmG Battlefire]

The great wall during the song dynasty wasn't very great... The mongols could easily use ropes and ladders to climb. A well built wall and high security in this day similar to the Berlin wall could easily stop immigrants in today's world.

45% of immigrant cross border by plane.

So we get rid of 55% sounds good to me.

17% by boat.
3% by train.
4% by tunnels.

Source: USCIS Volume 13 of Statistical study of Immigration.