Military uniform
History: A distinction should be made between uniforms and ethnic dress. If a particular people or culture favoured a distinctive dress style this could easily create the impression of uniformly dressed warriors. The issue is further complicated by the distinctive features (weapons, armour, fighting style and native dress) of particularly effective warrior classes often being copied. Thus the distinctive and colourful clothing of the Hungarian hussars became a model for hussar units all over Europe. The kilts and sporrans of Scottish Highland clans were distilled into regimental dress when the British Army started to recruit from these tribal groups.
Mercenary or irregular fighters could also develop their own fashions, which set them apart from civilians, but were not really uniforms. The clothing of the German Landsknechte of the 16th century is an example of distinctive military fashion. Special units such as Zouaves developed non-standard uniforms to distinguish them from troops of the line.

Antiquity: There are a few recorded attempts at uniform dress in antiquity, going beyond the similarity to be expected of ethnic or tribal dress. One example is the Spanish infantry of Hannibal who wore white tunics with crimson edgings. Another is the Spartan hoplite in his red garment, attributed by Plutarch "partly because it seems to be a manly colour and partly because (it) causes more terror amongst inexperienced foes". The Terracotta Army discovered in the tomb of the first Emperor of China (c. 200 BC) have a superficial similarity but closer examination shows up to seven different styles of armour, which do not appear to have been standardised within separate units.

Rome: The legions of the Roman Republic and Empire had a fairly standardised dress and armour, particularly from approximately the early to mid 1st century onward, when Lorica Segmentata (segmented armour) was introduced. However the lack of unified production for the Roman army meant that there were still considerable differences in detail. Even the armour produced in state factories varied according to the province of origin. Fragments of surviving clothing and wall paintings indicate that the basic tunic of the Roman soldier was of un-dyed (off-white) or red-dyed wool. Senior commanders are known to have worn white cloaks and plumes. Centurions – the century commanders who made up the long serving backbone of the legions – were distinguished by transverse crests on their helmets, various chest ornaments (phaleræ) corresponding to modern medals, torques (a symbol borrowed from the Gauls and also used as a military award), and the vine stick (Vitis) that they carried as a mark of their office.
While some auxiliary cohorts in the late Roman period had carried shields with distinctive colours or designs, there is no evidence that any one Roman legion was distinguished from another by features other than the numbers on the leather covers protecting their shields.

Post-classical era: The feudal system of Western Europe provided instances of distinguishing features denoting allegiance to one or another lord. These however seldom went beyond colours and patterns painted on shields or embroidered on surcoats. Orders of military monks such as the Knights Templar or Hospitaller wore mantles respectively of white (with red crosses on the shoulder) and of black (later red with white crosses)   over the usual pattern of armour for their periods. In the later part of the Medieval period instances of standardised clothing being issued for particular campaigns began to occur. English examples included the white coats worn by Norfolk levies recruited in 1296 and the green and white clothing that identified Cheshire archers during the 14th century.
The regular thematic (provincial) and Tagmata (central) troops of the Byzantine Empire (East Roman) are the first known soldiers to have had what would now be considered regimental or unit identification. During the 10th century, each of the cavalry "banda" making up these forces is recorded as having plumes and other distinctions in a distinctive colour. Officers wore a waist sash or pekotarion, which may have been of different colours according to rank.

Early modern era: 

European regimental dress: The styles and decoration of military uniforms varied immensely with the status, image, and resources of the military throughout the ages. Uniform dress became the norm with the adoption of regimental systems, initially by the French army in the mid-17th century. Before 1600 a few German and Dutch regiments had worn red or yellow coats. From about 1626 onwards some Swedish infantry had been issued with standard coloured dress under Gustavus Adolphus (hence his "yellow" or "blue" regiments). However, most levies of the 15th and 16th centuries wore civilian dress and regiments were dressed at the expense of their colonels in whatever style and colours the colonel preferred. Even Royal guards would sometimes only be issued with distinctive coloured or embroidered surcoats to wear over ordinary clothing. To help armies distinguish friend from foe, scarves, pieces of foliage, or other makeshift identification known as "field signs" would be worn, (a practice still recognised under international humanitarian law and the laws of war as a "distinctive sign"). Field signs were easily removed or donned, as in the example of John Smith, a squire on the Royalist side who at the Battle of Edgehill put on the orange scarf of the Parliamentarians and with no more elaborate disguise recaptured the royal standard from the Earl of Essex's own secretary.
By this time, in France at least, the general character of the clothes and accoutrements to be worn on various occasions was strictly regulated by orders. But uniformity of clothing was not to be expected so long as the "enlistment" system prevailed and soldiers were taken in and dismissed at the beginning and end of every campaign. The beginnings of uniform are therefore to be found in truly national armies, in the Indelta of Gustavus Adolphus, and the English armies of the English Civil War. In the earlier years of the latter, though the richer colonels uniformed their men (for instance, the Marquess of Newcastle's "Whitecoats" and King Charles's own red-coated Lifeguard of foot), the rustics and the citizens turned out for war in their ordinary rough clothes, donning armour and sword-belt. But in 1645 the Long Parliament raised an army for permanent service, and the colonels became officials rather than proprietors. The New Model Army was clothed in the civilian costume of the date—ample coat, waistcoat, breeches, stockings and shoes (in the case of cavalry, boots)—but with the distinctive colour throughout the army of red and with regimental facings of various colours and breeches of grey. Soon afterwards the helmet was replaced by a grey broad-brimmed hat. From the coat was eventually evolved the tunic of the mid-19th century, and the hat became the cocked hat of a later generation, which generally disappeared during the decade of 1800–1810 to reappear in the late 19th and early 20th century, by which time it had its original form of a "slouch-hat." For service in Ireland the New Model Army's red coat was exchanged for one of russet colour, just as scarlet gave way to khaki for Indian service in the 19th century. The Ironsides cavalry, however, wore buff leather coats and armour long after the infantry had abandoned them.
Thus the principle ever since followed — uniform coat and variegated facings — was established. By choice or convenience the majority of the corps out of which the New Model Army was formed had come to be dressed in red, with facings according to the colonel's taste. In Austria sixty years afterwards events took the same course. The colonels there uniformed their men as they saw fit, but had, probably to obtain "wholesale" prices, agreed upon a serviceable colour, pearl grey. When in 1707 Prince Eugene procured the issue of uniform regulations, few line regiments had to be re-clothed.  In France, as in England and Austria, the cavalry, still led by the wealthy classes rather than officered by the professional, was not uniformed upon an army system until after the infantry. But in 1688 six-sevenths of the French cavalry was uniformed in light grey with red facings; and about half the dragoon regiments had red uniforms and blue facings. The Marquis of Louvois, in creating a standing army, had introduced an infantry uniform as a necessary consequence. The native French regiments had light grey coats, the Swiss red, the German black and the Italian blue, with various facings. The French grey was probably decided upon, like the Austrian grey, as being a good "service" colour, which could be cheaply manufactured.

During the 18th century the normal military uniform in Europe comprised a standardised form of civilian dress (tricorn hat, long-skirted coat, waistcoat and breeches). One distinctively military feature were the long canvas gaiters which came up to mid-thigh and had multiple buttons. Dress was surprisingly standardised between European armies in cut and general outline. The distinction normally lay in colours: red coats for the British and Danes, light grey then white for the French, Spanish, and Austrian infantry, dark blue for the Prussians and Portuguese, green for the Russians, etc. Within each army different regiments were usually distinguished by "facings" — linings, turnbacks, and braiding on coats in colours that were distinctive to one or several regiments.