"If anyone wants your tunic (undergarment), let him have your cloak (outer garment) also."
IMO,this is merely to set an example on being kind to your enemies by finding a way to give them assistance, since they are obviously in need. This is not to say you bend completely to their will but find a way to appease them instead of strict retaliation (as taught in the OT).
Read down a few lines to 5:44
"Love your enemies, bless those that curse you, do good to those who hate you, and pray for those that spitefully use you and persecute you ..."
The first sentence could also be construed to mean that your enemies may want to attack your spirit but you should give them some of your wealth as well as sharing your spirit with them.
What are the coalition members now attempting to do? They seem to be sharing spirit, food and wealth with poor Muslem countries that supposedly hate the west. Coincidence?
Not from my viewpoint. Maybe it depends on how you want to view the scripture?