Suggested level bands for future events of this type - based on access to military units (I'm sure there is some building access that may adjust this a little, but here's my shot at it):
15 to 22 (recruits 15, bowman 17, militia 18)
23 to 35 (cav 23, longbow 25, soldiers 27)
36 to 47 (crossbow 36, elite soldiers 41)
48 to 53 (cannons 48)
54 to 62 (elite units beginning at 54)
63 to 75 (has access to all current deposits, etc, should have higher buildings established and somewhat upgraded)
Anyway, I expect the above is probably a more realistic set of bands where military adventures are concerned.

