If we pick terrorism, Marx and Engels' theory can help us understand that young males in the low social classes, who live in staggeringly unequal societies such as the Arab ones (Arab countries have very high GDP due to oil, yet alarming poverty rates) may feel oppressed and marginalized from the "game" of capital-building.
The problem of inequality in a society's economy might help us understand, in general, how religious fundamentalists have risen in these countries, and how the "Guerrillas" started decades ago in South America, all third world countries who veer their hatred towards the more privileged developed world. We can also remember that the Nazi movement saw its inception in a post-WWI Germany with such high rates of inflation that people brought wheelbarrows stacked with cash to the bakery when buying food, and how these people veered their anger onto a historically wealthy and productive people: the Jews. From this perspective, the true breeding pools of murderous ideologies and massive violent reactions always seem to be highly unequal societies.
On the other hand, Marx and Engels' view of Capitalism as a system that inherently causes suffering, where the rich are to blame for poverty itself and where there is always an oppressor and an oppressed, may divert us from the real problem regarding how demagogues weaponize the dispossessed. The young males that usually end up as militants for these causes feel disenfranchised by society as a whole, not only in the financial sphere of their lives but also socially and psychologically. The belief that the solution to social inequality is just to finance the poor so that they are economically equal to what Marxism would call the "bourgeoisie", is reductionist at best. Since the problem of being disenfranchised by society engulfs the entire individual in all aspects of life, inequality in society needs to be looked at as a problem that is educational, psychological and sociological besides just financial. This includes the fact that viewing the world in terms of only oppressor vs. oppressed is the sign of an immature psyche, the kind of psyche that a demagogue finds easy to manipulate.