if you start in canada you can watch it likely spread to greenland, then up the cold resistance and you should then see it travel to madagascar before they shut everything down
super addicting game, wow. I just completed nightmare. I'd say the trick is to be sleuthy in the early levels and don't use as many clicks as you have to. the exp you get will compound itself through the game with this tactic til the very end when you and your army shall be an unstoppable sumurai sweeper..thing lol. hope this helps.
 "Frontline Defense Special Ops"){kind=icon}
 "Mardi Gras Mayhem"){kind=icon}
 "Pandemic 2"){kind=icon}
 "Super Samurai Sweeper"){kind=icon}
 "Reeelz"){kind=icon}
 "Kingdom Rush"){kind=icon}