There does not seem to be any reason. You are better off attacking it and hopefully capturing it. 
There seems to be little reason to attack out of a city if you are besieged until you have numbers. Starvation and population reduction in cities is very slow. Defense has a huge advantage.
					There seems to be little reason to attack out of a city if you are besieged until you have numbers. Starvation and population reduction in cities is very slow. Defense has a huge advantage.

 
							
						 .  This ismore of an attrition/degradation strategy versus military conquest.
 .  This ismore of an attrition/degradation strategy versus military conquest.
							
						
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