Army of Isengard

The Army of Isengard, more commonly referred to as Saruman's army, was an almost immeasurable host 10,000 strong at least assembled around the fortress of Orthanc in Isengard by the corrupt Wizard Saruman, who allegedly humbly served the Dark Lord Sauron. The massive force was purposed by the mounting of the Enemy's assault through the destruction of the kingdom of Rohan, as well as the hunting of the Ringbearer.

A new Power has arisen
After renouncing the Wise and becoming the guileful servant of Sauron, Saruman set his sights on extending the reach of his long yearned-for power over the neighboring realm of his former allies. Promising plunder, conquest and bloodshed his minions and friends he then drew from all those who held disdain for Rohan, whether ill-favored Men or even feller wretched beings such as those of Orc-kind. From that hour, the forges built about the Tower of Orthanc never ceased to produce arms - not only glaives, helms, armor and blades but siege engines as well - for when the legions would march forth upon Rohan. With the army of Isengard, Saruman believed he could assure his Lord Sauron's rule in the coming age, or perhaps even his own.

By the time of the War of the Ring, the Wizard had began sending pillaging parties in incursions into the Rohirrim's territories, as well as to lie in wait on routes the Fellowship of the Ring was likely to take on their journey. One such Orc-troop camped at Amon Hen and ambushed the company, capturing the halflings Meriadoc Brandybuck and Peregrin Took and mortally-wounding the warrior Boromir. However, they were attacked on the road by the Rohirrim and forced to battle them near the eaves of Fangorn Forest, allowing the Hobbits to escape their captors.

Attack on Rohan
After gathering his full strength, Isengard was unleashed by Saruman at last in open-war against Rohan in the Battle of Helm's Deep. Aided by Wargs that were let loose across the plains around the fortress, scaling ladders and the sorcerous craft of Saruman, the thousands of Orcs were able to breach the defenses and push the hundred horse-riders into falling back deeper into Helm's Deep. The valiant Rohirrim commanded by King Théoden and Aragorn were able to hold out the vicious invaders for some time until the sun had arisen.

The two then led a charge against the Orcs, who in dread of the surprising counterattack briefly retreated. At that moment Gandalf arrived, joined by Prince Eomer and his riders, reinforcing the King's men at Helm's Deep. The forces of the free folk of Rohan combined, the army of Isengard could not prevail against the courage that stood against it and was utterly vanquished, what little remained of the Orcs not slain scattered in the wind.

Behind the sceneS
In J.R.R. Tolkien's The Lord of the Rings: The Two Towers, the army of Isengard is comprised not only of Orcs and Wargs, but also of Dunlendings, Orc-men and the fighting Uruk-hai which are visibly absent from Ralph Bakshi's animated film.