The laying a Country desolate with Fire and Sword, declaring War against the natural rights of all Mankind, and extirpating the Defenders thereof from the Face of the Earth, is the Concern of ever Man to whom Nature hath given the Power of feeling. (I.4)
Thomas Paine is certain that, in one way or another, Britain has already declared war on America. Now it's just a matter of fighting back. To make anyone queasy about the idea of war feel better, Paine states that a war from American independence will affect freedom all over the world.