Nuclear weapons exist and have been constructed, but do not have a significant position in most nation's strategic doctrine. The primary purpose of war in TFS remains the seizure--or defense--of resources, land, and infrastructure, all of which are harder to obtain from your opponent if nuclear weapons are employed in an offensive role. Instead, various empires prefer to first clear an area of its civilian and military population with gas, then move in their own troops to occupy and fortify. Gas doesn't destroy railways or erase mines of precious ore, you see.
For this reason, the British methodology of strategic bombardment across the United States during the Third Anglo-American War is considered quite brutal, as was their response to the uprising in Bengal, and is probably c=the closest equivalent to M.A.D. in this world. The message from London is clear: any affront to His Majesty will be met with disproportionate decimation.