Standing army
History: 

Ancient history: 

Mesopotamia: Sargon of Akkad, the founder of the Akkadian Empire, is believed to have formed the first standing professional army. Tiglath-Pileser III of Assyria (ruled 745–727 BC) created Assyria's first standing army. Tiglath-Pileser III disbanded militias and instead paid professional soldiers for their services. His army was composed largely of Assyrian soldiers but was supplemented with foreign mercenaries and vassal states. The standing army he created was the most sophisticated administrative and economic institution of its time, and was the engine of Assyrian economy which capitalized on warfare.
Ancient Persia
Cyrus the Great formed the first professional army of Persia. The composition of the army varied and developed in the course of time. The empire's great armies were, like the empire itself, very diverse. Its standing army was composed of Persians (the bravest people of empire according to Herodotus) and Medes. This standing army, which may have been reviewed every year by the king or his representative, is called kāra in the inscriptions. At the heart of this army was its elite guard, The 10,000 Immortals. Herodotus describes that if any of these guardsmen drops out owing to death or disease, a substitute is immediately supplied and the number again filled. Thousands of these 10,000 guardsmen composed the royal bodyguards in the palace, their insignia were golden apples or pomegranates at the butts of their spears (accordingly they are named “apple-bearers” by Heraclides Cumaeus).

Ancient Greece: In ancient Greece, the city-states' (poleis) armies were essentially drafted citizen militias. The exception was in ancient Sparta, which had a standing army that trained year-round (and not only in summertime). Through the 5th century, they comprised the only professional soldiers in ancient Greece, aside from hired mercenaries. However, the Spartan army commonly consisted of helots (serfs), who considerably outnumbered the Spartiates, as well as numerous allies of Sparta.
Philip II of Macedon instituted the first true professional Hellenic army, with soldiers and cavalrymen paid for their service year-round, rather than a militia of men who mostly farmed the land for subsistence and occasionally mustered for campaigns.

Ancient China: The Western Zhou maintained a standing army, enabling them to effectively control other city states and spread their influence. Unlike the Western Zhou, the Eastern Zhou initially did not have a standing army. Instead they drafted militias from around 150 city states. While the Eastern Zhao did not initially maintain a standing army, the state of Jin became the first to do so in 678 BCE. The first professional army in China was established by the Qin dynasty in 221 BCE, which ushered Imperial China. Under the Qin dynasty, wars were fought by trained vocational soldiers instead of relying on temporary soldiers.

Ancient India: In Ancient India, warfare was first attested during the Vedic period. However, warfare was primarily waged between various clans and kingdoms solely by the kshatriya class during times of conflict. True standing armies in India developed under the Mahajanapadas, which relied on paid professional soldiers year round. The most prominent of the Mahajanapadas was the Kingdom of Magadha. It is accepted that the first standing army of India was created in Maghada by the ruler Bimbisara.

Ancient Rome: Under the reign of Augustus, the first Roman emperor, a standing professional army of the Roman Empire was gradually instituted, with regularized pay. This professional force of legionaries was expensive to maintain, but supported the authority of the empire, not only as combat troops but also as provincial police forces, engineers, and guards. Legionaries were citizen volunteers entitled to a discharge bounty upon 25 years of honorable service; supplementing the legions were the auxilia, auxiliary forces composed of non-citizens in the provinces who typically earned citizenship as a reward for service.

Post-classical history: 

Ottoman Empire: The first modern standing armies on European soil during the Middle Ages were the Janissaries of the Ottoman Empire, which were formed in the 14th century under Sultan Murad I.

France: The first Christian standing army since the fall of the Western Roman Empire to be paid with regular wages, instead of feudal levies, was established by King Charles VII of France in the 1430s while the Hundred Years' War was still raging. As he realized that France needed professional reliable troops for ongoing and future conflicts, units were raised by issuing "ordonnances" to govern their length of service, composition and payment. These compagnies d'ordonnance formed the core of the French gendarmes that dominated European battlefields in the late 15th and early 16th centuries. They were stationed throughout France and summoned into larger armies when needed. Provisions were also made for franc-archers and foot soldiers raised from the non-noble classes, but those units were disbanded at the end of the Hundred Years' War.
The bulk of the infantry for warfare was still provided by urban or provincial militias, raised from an area or city to fight locally and named for their recruiting grounds. Gradually these units became more permanent, and in the 1480s, Swiss instructors were recruited and some of the 'bandes' (militia) were combined to form temporary 'legions' of up to 9,000 men. The men would be paid and contracted and would receive training.
Henry II further regularised the French army by forming standing infantry regiments to replace the militia structure. The first, the Régiments de Picardie, Piémont, Navarre and Champagne, were called Les Vieux Corps (The Old Corps). It was normal policy to disband regiments after a war was over to save costs. The Vieux Corps and the king's own household troops (the Maison militaire du roi de France) were the only survivors.

Hungary: The Black Army, established in 1462 by Hungarian king, Matthias Hunyadi was the first Central/Eastern European standing army. However, while the Black Army was certainly the first standing field army in that part of Europe, Hungary in fact had maintained a permanent army in the form of garrisons of border fortresses since the 1420s.
Matthias recognized the importance and key role of early firearms in the infantry, which greatly contributed to his victories.
Every fourth soldier in the Black Army had an arquebus, which was an unusual ratio at the time. The high price of medieval gunpowder prevented them from raising it any further. The main troops of the army were the infantry, artillery and light and heavy cavalry.  The function of the heavy cavalry was to protect the light armoured infantry and artillery, while the other corps delivered sporadic, surprise assaults on the enemy.

Songhai Empire: In West Africa, the Songhai Empire under the Askia Mohammad I (1493–1528) possessed a full-time corps of 40,000 professional warriors. Al-Sa'di, the chronicler who wrote the Tarikh al-Sudan, compared Askia Mohammad I's army to that of his predecessor; "he distinguished between the civilian and the army unlike Sunni Ali [1464–92] when everyone was a soldier." Askia Mohammad I is said to have possessed cynical attitudes towards kingdoms that lacked professional armies like his, notably in reference to the neighboring kingdoms in the land of Borgu.

Majapahit Empire: The Majapahit thalassocracy was recorded by a Chinese observer as having 30,000 full-time professional troops, whose soldiers and commanders were paid in gold. This shows the existence of a standing army, an achievement that only a handful of Southeast Asian empires could hope to achieve.: 185 : 467  In addition to these professional soldiers, Majapahit was strengthened by troops from subordinate countries and regional leaders.: 277  As was common in Southeast Asia, Majapahit also used a levy system, in fact, the majority of the Majapahit troops were a levy.: 111–113

Spain: The Spanish Empire tercios were the first Spanish standing units composed of professional soldiers. Their pike and shot composition assured predominance in the European battlefields from the 16th century to the first half of the 17th century. Although other powers adopted the tercio formation, their armies fell short of the fearsome reputation of the Spanish, whose core of professional soldiers gave them an edge that was hard for other states to match.

England and Great Britain: Prior to the influence of Oliver Cromwell, England lacked a standing army, instead relying on militia organized by local officials, private forces mobilized by the nobility and hired mercenaries from Europe. This changed during the English Civil War, when Cromwell formed his New Model Army of 50,000 men. This professional body of soldiers proved more effective than untrained militia, and enabled him to exert control over the country. The army was disbanded by Parliament following the Restoration of the Monarchy in 1660, and the Cromwellian model was initially considered a failure due to various logistical and political problems with the force.
The Militia Act 1661 prohibited local authorities from assembling militia without the approval of the king, to prevent such a force being used to oppress local opponents.