Were the Nazis any more ruthless than ISIS?
No, but the comparison really isn't valid.
Anyone remotely interested in this subject needs to study 4GW, Fourth Generation Warfare. It's always been around in some forms (guerilla fighting among them) but we've been in a 4GW environment, on a large scale, pretty much since Vietnam and definitely since the first WTC bombing in the early '90s.
The problem for the West is that the old rules that many people still think govern warfare no longer apply and haven't applied for a long time. They really started to dissolve with
"total war." But the modern enemy (many of them) do not subscribe to ANY historically understood command and control structure, but instead are autonomous, anonymous individuals or small cells widely dispersed and united around an idea...for example, a global caliphate. This strategy can be good, depending on one's perspective (the Colonists can be said to have engaged in 4GW by shooting from behind trees at British rank and file soldiers), but it is very dangerous to have to face. It is precisely why civilians are now ruthlessly targeted.
It is also why Western governments who actually want to fight them have so much difficulty doing so: with rare exceptions no Western military is geared mentally or structurally to respond effectively to such an amorphous, decentralized threat, especially when its adherents are willing to die for the cause.
Some say 4GW does not exist or that the threat is overstated. They are dead wrong. Recent events both in Europe and the U.S. prove it.
Fourth-generation wars are lengthy -- measured in decades rather than months or years. . . Strategically, 4GW attempts to directly change the minds of enemy policy makers. This change is not to be achieved through the traditional method of superiority on the battlefield. The first- through third-generation of destroying the enemy’s armed forces and his capacity to regenerate them is not how 4GW enemies will attack . . . Both the epic, decisive Napoleonic battle and the wide-ranging, high-speed maneuver campaign [German blitzkreig] is irrelevant to them. Their victories are accomplished through the superior use of all available networks to directly defeat the will of the enemy leadership, to convince them their war aims are either unachievable or too costly. These networks will be employed to carry specific messages to our policy makers and to those who can influence the policy makers. -- COL Thomas X. Hammes, USMC, The Sling and the Stone, p. 208
The main way they do this today is by targeting civilians. That works VERY well in democratic societies. It also does not help that we have so many leftists in positions of power, leftists who want to weaken the West into failure by any means necessary in order to replace it. In their minds, Mohammedans are only one means to that end...hence the destruction of borders and importing them en masse. The global Left is riding a ravenous tiger, stupidly, but they'll learn that too late.
http://sipseystreetirregulars.blogspot.com/2013/04/tyrants-beware-4th-generation-warfare.html