Wargaming comes in all flavours and covers a very wide range of time periods. Nevertheless, a few classic periods emerge as summary categories. These categories are in part the result of theme and timing (for historical games) but also defined by the style of warfare in each period. The time periods below are very approximate and centered on European theatres of war. There are many wargaming opportunities such as ancient asian conflicts, colonial wars in Africa and the Americas, and so forth. All of these areas tend to follow the same progression of periods but the dates often vary significantly from those provided below (e.g. Japan had a much longer medieval period due to the relatively late introduction of gun powder weapons).
As the name implies, fantasy games are not historical but rather imaginary periods with dragons, daemons and magic. Popular examples are the Warhammer Fantasy Battle game, Mordheim and Warmachine/Hordes. Fantasy games often include strong references to ancient and medieval history to provide players with an easy point of reference. For example, a dragon in the Warhammer world might be facing a distinctly “medieval Germanic” knight. In addition to historical geographic and cultural references, fantasy games often introduce a broad range of historical technology – often without the coherence of real history (e.g. bow and arrow, early gun powder and steam engines might all appear in the same setting). The thematic aspect of fantasy games is broadly divided into “High Fantasy” where the fantasy elements are common-place (e.g. the Warhammer world where every village has mythical elements magic is everywhere), and “Low Fantasy” where most aspects of the setting are historical or “normal” and fantasy elements are rare.
Ancients (~5000BC to ~ 400AD)
The ancients period covers a large portion of human history, from the beginning of organised civilization to the approximately the fall of the Roman Empire. Player and rule systems will argue endlessly about the precise year of the end point, partly because the dividing line is definitely blurry. The key feature of this period is that battles are fought and decided primarily by strength of arm: Different sub-periods emphasis specialised fighting styles such as the chariots of the early Egyptians, the Greek phalanxes and the Roman Legions but the fundamental dynamics remain the same: Warriors in formations trying to push and rout opposing formations. With some exceptions, cavalry was a support force during this period and battles were decided by the fighting prowess, discipline, mass and morale of infantry units.
Dark Ages (~400AD to ~800AD)
The Dark Ages show the transition from military formations to individual warriors as the main element of battles. The Germanic warrior tribes, Vikings, Arthurian Celts and Picts, all fought largely in the same way: Individual fighters trying to hit each other with blunt, sharp or pointy objects. Another distinction of this period is that warfare assumed a distinctly local character. Gone were the days when empires wages wars across continents. From a gaming perspective, the transition from Ancients to Dark Ages is gradual and in some regions occurs very late (especially in Eastern Europe and the Middle East where the Roman influence lingered a lot longer).
Medieval Period (~800AD to ~1400AD)
The emergence of knights, fed and armed by the feudal system, reversed the power dynamics of warfare. Instead of mobile support, cavalry became a crushing sledgehammer that dominated the field of battle. This period also re-introduced a broader scope to warfare, in particular along the west-east conflicts of the crusades which also introduces religion as a serious point of division. Most fantasy games use the medieval period as their anchor point and thus feature similar rock/paper/scissor dynamics (e.g. cavalry crushes infantry, shock infantry beats missile infantry, missile infantry skewers cavalry).
Pike and Shot (~1400AD to ~ 1700AD)
In an effort to counter the strength of armoured knights, the humble infantrymen turn first to the pike (a very long spear or halberd) and shortly after towards high power missile weapons. Both weapon types, if fielded in disciplined formation, were able to defeat armoured knights and thus ended their era of dominance for ever. The choice of missile weapon was regional initially (e.g. the English longbow, French/Italian crossbows, etc.) but all regions ultimately converged on gun power weapons. Warfare became a shooting match with shock infantry and cavalry often only in place to provide defensive capability to the missile troops. As a result, many of the features of the Ancient period such as tightly grouped formations and specific tactical layout of units re-emerged (e.g. Swedish checker formations during the 30 Years War, etc.). Artillery starts to appear on the battlefield but the low rate of fire leaves it in a role similar to missile troops.
Musket & Rifles / Napoleonic (~1700AD to ~1900AD)
Often named after the showcase conflict during this period (Napoleon’s campaigns), this period also usually includes surrounding conflicts such as the American War of Independence, Civil War and colonial wars in Africa. The invention of the bayonet as eliminated the need for dedicated pike infantry to protect the missile troops and shock infantry has consequently disappeared completely from the battlefield. Lines of infantry, armed with gun powder weapons, are facing each other in tight formations and bang away at each other. Cavalry remain in a support function and artillery is a distinctly independent branch of service in yet another support role.
World Wars / Modern (~1900AD to ~1950AD)
Many gamer and rule systems treat the two World Wars and later conflicts as very distinct periods. At the lower level of game play they certainly offer different dynamics with the trench warfare of WW1, the sweeping Blitzkrieg of WW2 and the “pin-point” theme of modern battles. That said, at the macro level the entire period has a common foundation: Rapid fire weapons such as machine guns make infantry formations obsolete, shock cavalry has returned in the form of armoured tanks, and artillery dominates most engagements in terms of destructive power.
Similar to the Fantasy “period”, science fiction games using an imaginary world with space crafts, non-human races and often some form of “magic” (e.g. psychic powers, “the force” in Star Wars, etc.). The setting is often dark and brooding to provide reasons for wargaming activities. For similar reasons, technology on the battlefield is often limited for some reason (e.g. Warhammer 40k armies can fly through the galaxy in giant space ships but troops smash each other with swords).