The Committees of Safety and Observation began immediately to gather arms, and later to arrest inimical or suspected persons and bring them to trial.

With few exceptions the inhabitants of Orange and Ulster Counties were loyal, earnest and active for the cause of Independence. In the early years of the war the militia was efficient in guarding the frontiers, constructing Highland forts and placing obstructions to navigation in the Hudson River; and two of the companies took part in the expedition to Canada of 1775. In 1776 one-fourth of the militia of the two counties was "drawn out for the defense of the State" and stationed along the Highlands. They consisted of two regiments from Orange commanded by Colonel Isaac Nicoll, and one from Ulster commanded by Colonel Levi Paulding. In December, after the British had captured New York, a more general requisition was made, and men were obliged to leave their families and stock unprovided for, which caused great disaffection for a time; but after General Washington's victory at Trenton they were permitted to return home.

In 1777 George and James Clinton were in command on the west side of the Hudson, and General Putnam on the east side. Burgoyne, with an army of 3,000 men, marching down from Canada, had reached Saratoga, and Howe, with another army, was marching to capture Philadelphia, when, about September 20, 3,000 British and Hessian soldiers arrived in New York and joined the army of Sir Henry Clinton. Thus reinforced Clinton soon started to force his way up the Hudson, and on October 6, approached Forts Montgomery and Clinton, defended by some 400 of Colonel Du Bois's Regiment and Lamb's Artillery, and about 200 militia, mostly from Orange and Ulster Counties. They made a gallant defense, but finally overwhelmed by superior numbers, were obliged to retreat, leaving behind them 300 in killed, wounded and prisoners. In Governor Clinton's report to General Washington of the fight at Fort Montgomery he said that Sir Henry Clinton commanded in person; that the enemy was repeatedly driven back by grape shot from a field-piece and the well-directed fire of musketry during their approach; that the militia retreated to the fort, when a demand to surrender was refused; and that the enemy's superior numbers finally forced the works on all sides. If expected reinforcements had reached the fort it was believed that the enemy would have been defeated. Many militiamen were in the mountains, but their communications had been cut off. There were not more than 600 men in both the forts, while the attacking army numbered 3,000. Governor Clinton escaped across the Hudson, and many of his men were bayoneted after the works were taken. Du Bois's Continental Regiment and Lamb's Artillery bore the brunt of the fight. The following other regiments were represented in small numbers; Colonel Allison's from Goshen, commanded by himself; Colonel James Clinton's from New Windsor, commanded by Lieutenant Colonel James McClaughry; Colonel Harbourg's from Newburgh, commanded by Colonel Masten; Colonel Jesse Woodhull's from Cornwall, commanded by Colonel Du bois.

Sir Henry Clinton's ships moved on up the Hudson, and Putnam's and Clinton's troops followed. The British Commander caused Kingston to be burned, and here, receiving the news of Burgoyne's surrender, turned back. His army tarried a few days in the Highlands to complete the destruction of the forts, and then sailed to New York, and the militia returned home.

The Indians on the western frontier of Orange and beyond were still nursing grievances against the colonists, and were easily won over to the British side by diplomatic agents. Their depredations began again in 1777, when the family of a Mr. Sprague in the northern part of the Minisink was attacked and some of them taken prisoners. Next they killed some of the family of a Mr. Brooks, and took the rest prisoners. In 1778 the upper Minisink was invaded by about 100 Indians, under the famous warrior chief, Brandt, and on Oct. 13 they attacked two dwellings, killed three persons and destroyed much grain and stock. The settlers repaired to the forts of Gumaer's and De Witt's, and the Indians after following and firing a few times at them from a distance, went away.

The Committee of Safety for Minisink in 1778 consisted of Benjamin DePuy, Philip Swartout and Ezekiel Gumaer, and they ordered the erection of five forts, three in the upper neighborhood, and two in the lower. These could not accommodate all of the fifty families in what is now Deer Park, and many women and children were sent to the older settlements. Scouting parties were sent out under command of Captain Bezaliel Tyler, and persons suspected of aiding the Indians were imprisoned or banished. Small companies of nine months militia were obtained to garrison the forts.

The massacre of Wyoming in July, and the horrible cruelties practiced upon some of the prisoners, had caused grave apprehensions, and these were increased by the coming of Brandt and his Indians in October. Count Pulaski and his cavalry legion were sent to Minisink, and remained there during the winter of 1778-9, and Colonel Van Cortlandt's Regiment was sent to Wawarsing. In the spring Count Pulaski and his legion were ordered to South Carolina, and on July 19 Brandt, aware of the poorly defended Minisink, came with sixty-five Indian warriors and twenty-seven Tories disguised as Indians, to the lower section, now Deer Park, south of the Neversink and while the settlers were asleep set fire to several dwellings. Some of the inmates were killed as they were fleeing and others were taken prisoners. The cattle were driven off, and much booty carried to Brandt's headquarters, Grassy Brook, on the Delaware. When news of the murderous raid was received by the militia, a council was held by Lieutenant-Colonel Tusten of Colonel Allison's Goshen Regiment, Colonel John Hathorn of the Warwick Regiment, and Captain Meeker of the New Jersey militia, and contrary to Tusten's advice, it was decided to march against the Indians with such numbers of men as could be quickly brought together. Meanwhile Brandt's force had been increased to about 300 Indians, and 200 Tories painted to resemble Indians. The small band of militiamen, commanded by Colonel Hathorn, marched to the hills overlooking the Delaware near the mouth of the Lackawaxen, and then discovered Brandt and his warriors three-fourths of a mile away. Colonel Hathorn prepared to attack them, but Brandt outmaneuvered him, and cut off fifty of his men, leaving only ninety in the fight that followed. Brandt got in their rear, and hemmed them in on a rocky slope, with the advantages of position and more than five times as many men. When their ammunition was exhausted they formed in a hollow square to fight with clubbed muskets, but the square was soon broken and the men sought safety in flight. Tusten was killed by the Indians while dressing wounds of his men behind a rock, as were also seventeen wounded men with him. Others were shot or drowned in trying to swim across the Delaware. Only about thirty survived.

In Colonel Hathorn's report of the fight to Governor Clinton he says that "the enemy repeatedly advanced to from forty to one hundred yards distance and was as repeatedly repulsed"; that his men "defended the ground nearly three hours and a half and during the whole time one blaze without intermission was kept up on both sides." This was at the last stand on the slope. Hathorn's men had been firing for five hours, when, ammunition being almost exhausted, he ordered that no one fire "without having his object sure." Soon they were forced to retreat down the hill towards the river, and scattered, every man for himself. Colonel Hathorn further says:

"The Indians were under the command of Brandt, who was either killed or wounded in the action. They burnt Major Decker's house, barn and mill, James Van Vlock's house and barn, Daniel Vanoker's barn (here were two Indians killed from a little fort around the house, which was saved). Esquire Cuykindall's house and barn, Simon Westfall's house and barn, the church, Peter Cuykindall's house and barn; Martinus Decker's fort, house, barn and saw-mills, and Nehemiah Patterson's saw-mill; killed and scalped, Jeremiah Vanoker, Daniel Cole, Ephriam Ferguson and one Tavern, and took with them several prisoners, mostly children, with a great number of horses, cattle and valuable plunder. Some of the cattle we rescued and returned to the owners."