Incendiary comes from Middle English incendiarie, which came from Old French incendiaire.  This in turn came from Latin incendiārius (“setting alight”), from incendium (“destructive fire”), from incendō (“I set on fire, kindle”), from in- (“into, in, on, upon”) + candeō (“I am hot”). 

Early thermal, or incendiary, weapons, which used heat or burning action to destroy or damage enemy personnel, fortifications or territories, were employed in warfare during the ancient and post-classical periods (approximately the 8th century BC until the mid-16th century AD).  

The English word "incendiary" was The word "incendiary" in English was first recorded in the 15th century. It originally described something capable of causing fire, physically (like a weapon).  The figurative sense of "enflaming passions" emerged in the 17th century, around 1610-1611. 

Examples of "incendiary" used in a sentence: 
"The fire was started by an incendiary bomb." 
"The radical polemics of the panels must have seemed incendiary in the 1930s." 
*"All weapons are strictly prohibited from the stadium, from small knives to incendiary devices." 
*"The principal's incendiary remarks about their clothes were not appropriate for the students to hear." 
*"His team continued to clear the building and toss flares into corners as they sought out any living insurgents or incendiary devices.
*"The politician did not expect the responses to his town hall address to be so incendiary."
*"The man's rude and incendiary comments to the restaurant staff led to him being forced to leave." 

Incendiary language used in arguments, especially political, can, and often do, result in individual physical altercations, donnybrooks, and even murder. 

Just the facts:

INCENDIARY Definition & Meaning - Merriam-Webster