The Khmer empire was a powerful state in South East Asia, formed by people of the same name, lasting from 802 CE to 1431 CE. At its peak, the empire covered much of what today is Cambodia, Thailand, Laos, and southern Vietnam.
By the 7th century CE, Khmer people inhabited territories along the Mekong river -the world’s seventh longest river - from the delta to roughly the modern Cambodia-Laos border, plus the region between that river and the great Tonle Sap lake to the west and the area running along the Tonle Sap river (which runs from the lake to the sea, joining the Mekong in the delta). There were several kingdoms at constant war against each other, with art and culture heavily influenced by India due to long established sea trade routes with that subcontinent.
I hope this helps
As I recall it was rolled-steel girders riveted together, probably from shipbuilding, together with steam-powered winches and an abundance of cheap steel. As opposed to European cathedrals erected with animal-powered winches and with more expensive forged iron bracing (one of the big cathedrals has a kind or iron corset to keep the walls from bursting outwards).
Because it could roll over bombed out landscapes and keep penetrating the opposing force. Hope that helped! ;)
In this passage, the type of warfare being described by the author is "chemical warfare".
