At the end of the 16th century, the three main infantry types in European armies, pikemen, arquebusiers and musketeers, all wore helmets. These latter had, by the beginning of the 17th century In England, Pikemen gave up their 'pots', and their cuirasses in the 1670s. This was the culmination of trends towards levening the pikeman's burden- First by disposing of his splints, or arm-guards early in the century, and, by mid-century, discarding the tassets, or leg-guards. There are several reasons for this- Namely that armor had, by the late 17th century, become something of an unnecessary encumbrance. Furthermore, the pikeman's role, too, was rapidly becoming obsolete. The musketeer, with the introduction of the plug, and later socket bayonet, could repel cavalry.

In North America, infantry armor followed the same course that it did in Europe. In the early years of the 17th century, the nature of warfare in the rugged frontier often necessitated the wearing of armor for protection, particularly against indigenous arrows. In his battle with the Iriquois, Samuel de Champlain wore a 'light armor' consisting of a cuirass, tassets, and helmet, but no splints. The garrison of Jamestown wore similar 'light armors' according to the Martial Laws of 1611, with the addition of quilted 'bases' around the legs.Within the English North American colonies, armor was worn later in Virginia (till around 1650, with the cessation of hostilities with the Powhatan peoples) than it was in New England.

Similar processes were followed in the cavalry. Three main types of cavalry existed in Early Modern Armies- The heavily armored cuirassier, (who wore a suit of three-quarters armor, 'proofed' to withstand bullets, and consequently enormously heavy and ruinously expensive), the harquebusier (who often wore only a back and breast plate worn over a buff leather coat, with a 'lobster-tail pot' helmet), and the dragoon (who were equipped as musketeers, often wearing no armor at all). Over the course of the century, the lightly armored harquebusier replaced the heavily-armored cuirassier, as emphasized by the assumption of the generic title of 'Horse'. By the end of the century, regiments of horse lost their armor- Wearing only buff leather coats. John Churchill, the Duke of Marlborough and celebrated general of the English forces in the early 18th century, later ordered his regiments horse serving in the War of the Spanish Succession wear cuirasses.

In some aspects, the helmet never left military service. English Dragoons during the War of the Spanish Succession wore iron skull-caps beneath their hats. Helmets proper did not have long to re-appear on the battlefield. Irregular light cavalry hailing from the frontiers of Hungary, Poland, Ukraine and Croatia were entered European armies at this time. It did not take long for home-grown troops to imitate these hinterland warriors. These warriors took on all manner of romantic dress, either fanciful, or in exaggerated imitation of the genuine article. By 1743, the light dragoons of the French Voluntaires de Saxe had adopted a pseudo-classical helmet with a horse-hair crest, and bearing a Gorgon's head on the front! John Mollo, writing in Military Fashion, states that the helmet may have owed it's theatrical design to the Marshal's actress mistresses. A regulation helmet adopted for all French dragoons in 1763, was essentially similar, though with the gorgon's head restricted to the front of the crest. The light troops added to British regiments in 1755 imitated their French counterparts in adopting the neo-classical headgear, albeit theirs was in leather, not brass. This helmet was adopted in the light dragoons regiments, first raised in 1759.

You mentioned the American revolution in your post- Indeed, helmets were worn by both American and British cavalry regiments in the war. In particular, the second continental Light Dragoons (Sheldon's Dragoons) wore brass helmets in the French Fashion for at least some part of the war.^1 Leather helmets were worn by other regiments of light dragoons, as well as the partisan corps of Armaund, Pulaski, and Lee.

By far the most famous article of military clothing to come out of the war was the Tarleton Helmet. This helmet, made famous by Banastare Tarleton's British Legion, was peaked, with a leather crown and a bearskin crest passing from front to rear. It attained popularity in both the British army, where it was made regulation for all Light Dragoons in 1784 and some Light Comapnies, to say nothing of it's widespread use in Volunteer and Yeomanry regiments, and in the Revolutionary French Army, where the Casque a la Tarleton was made regulation for the Demi-Brigades.

The French Revolutionary Wars, and the Napoleonic Wars which followed them, saw, if anything, the further dissemination of helmets throughout Europe's armies. With the ascension of Napoleon as Emperor of the French, the neo-classical helmet was adopted by French Cuirassiers and Carbineers. During the 19th century, practically all European cavalry, and, in the aftermath of the Franco-Prussian War, numerous regiments of Infantry, wore some form of helmet. These were, however, largely decorative.

Sources:

Barthorp, Michael. British Cavalry Uniforms since 1660 (Blandford, 1984)

-- British Infantry Uniforms since 1660 (Blandford, 1982)

Chapman, Frederick T. and John R. Elting. "The Provost Company of Light Dragoons, 1778-1783," in Military Uniforms in America: The Era of the American Revolution, ed. John R. Elting. (Presidio Press, 1974)

McBarron, H. Charles and Frederick P. Todd. "2nd Regiment of Continental Light Dragoons, 1780" in Military Uniforms in America: The Era of the American Revolution, ed. John R. Elting. (Presidio Press, 1974)

Mollo, John. Military Fashion (G.P. Putnam, 1972)

-- Uniforms of the American Revolution (Macmillan, 1975)

Peterson, Harold Leslie. Arms and Armor in Colonial America (Courier Dover Publications, 2000)

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^1 Long enough for the artist John Trumbull to illustrate one in his painting of the surrender of General Burgoyne. Trumbull, however, must be taken with caution when dealing with military uniforms. Though he served in the war, memory, or mode, blurred his memory in depicting military dress.