Siege

A siege is a military blockade of a city or fortress. The purpose is to conquer by starvation, lack of water, or by a well-prepared assault. 

Siege warfare is a form of constant, low-intensity conflict. The defender inside has a strong, static, defensive position. Negotiation between combatants is common.

A siege happens when the attacker gets to a city or fortress which cannot be taken by storm, and which refuses to surrender. Sieges block the  supplies and reinforcements or escape of men. Siege engines, artillery bombardment, and undermining are frequent. Deception and treachery are common.

Sieges can be decided by starvation, thirst, or disease. This form of siege can take many months or even years, depending upon the size of the stores of food the fortified position holds. 

Well known sieges were:

 Siege of Petersburg
 Siege of Yorktown
 Siege of Odessa
 Siege of Orleans
 Siege of Fort Zeelandia
Siege of Leningrad
 Siege of Tobruk
 Siege of Vicksburg