Declaration of war in the context of "Covert operation"

During the Classical era and Hellenistic era of Classical Antiquity, many Hellenic city-states had adopted democratic forms of government, in which free (non-slave), native (non-foreigner) adult male citizens of the city took a major and direct part in the management of the affairs of state, such as declaring war, voting supplies, dispatching diplomatic missions and ratifying treaties. These activities were often handled by a form of direct democracy, based on a popular assembly. Others, of judicial and official nature, were often handled by large juries, drawn from the citizen body in a process known as sortition.

By far the most well-documented and studied example is the Athenian democracy in Athens. However, there are documented examples of at least fifty-two Greek city-states including Corinth, Megara, and Syracuse that also had democratic regimes during part of their history. According to Ober (2015), the proportion of Greek city-states with democratic regimes gradually increased from the mid 6th century BC to the end of the 4th century BC, when perhaps half of the one-thousand Greek city-states in existence at the time had democratic regimes.

The Second Punic War (218 to 201 BC) was the second of Punic Warsthree wars fought between Carthage and Rome, the two main powers of the western Mediterranean in the 3rd century BC. For 17 years the two states struggled for supremacy, primarily in Italy and Iberia, but also on the islands of Sicily and Sardinia and, towards the end of the war, in North Africa. After immense materiel and human losses on both sides, the Carthaginians were once again defeated. Macedonia, Syracuse and several Numidian kingdoms were drawn into the fighting, and Iberian and Gallic forces fought on both sides. There were three main military theatres during the war: Italy, where Hannibal defeated the Roman legions repeatedly, with occasional subsidiary campaigns in Sicily, Sardinia and Greece; Iberia, where Hasdrubal, a younger brother of Hannibal, defended the Carthaginian colonial cities with mixed success before moving into Italy; and Africa, where Rome won the war.

The First Punic War had ended in a Roman victory in 241 BCE after 23 years and enormous losses on both sides. After the war Carthage expanded its holdings in Iberia where in 219 BCE a Carthaginian army under Hannibal besieged, captured and sacked the pro-Roman city of Saguntum. In spring 218 BC Rome declared war on Carthage, beginning the Second Punic War. Later that year, Hannibal surprised the Romans by marching his army overland from Iberia, through Gaul and over the Alps to Cisalpine Gaul (modern northern Italy). Reinforced by Gallic allies he obtained crushing victories over the Romans at the battles of Trebia (218) and Lake Trasimene (217). Moving to southern Italy in 216 Hannibal defeated the Romans again at the battle of Cannae, where he annihilated the largest army the Romans had ever assembled. After the death or capture of more than 120,000 Roman troops in less than three years, many of Rome's Italian allies, notably Capua, defected to Carthage, giving Hannibal control over much of southern Italy. As Syracuse and Macedonia joined the Carthaginian side after Cannae, the conflict spread. Between 215 and 210 BC the Carthaginians attempted to capture Roman-held Sicily and Sardinia, but were unsuccessful. The Romans took drastic steps to raise new legions: enrolling slaves, criminals and those who did not meet the usual property qualification; this vastly increased the number of men they had under arms. For the next decade the war in southern Italy continued, with Roman armies slowly recapturing most of the Italian cities that had joined Carthage.

The Falklands War (Spanish: Guerra de las Malvinas) was a ten-week undeclared war between Argentina and the United Kingdom in 1982 over two British Overseas Territories in the South Atlantic: the Falkland Islands and its territorial dependency, South Georgia and the South Sandwich Islands. The conflict began on 2 April 1982, when Argentina invaded and occupied the Falkland Islands, followed by the invasion of South Georgia the next day. On 5 April the British government dispatched a naval task force to engage the Argentine Navy and Air Force before making an amphibious assault on the islands. The conflict lasted 74 days and ended with an Argentine surrender on 14 June, returning the islands to British control. In total, 649 Argentine military personnel, 255 British military personnel and three Falkland Islanders were killed during the hostilities.

The conflict was a major episode in the protracted dispute over the territories' sovereignty. Argentina claimed (and maintains) that the islands are Argentine territory, and the Argentine government thus described its military action as the reclamation of its own territory. The British government regarded the action as an invasion of a territory that had been a Crown colony since 1841. Falkland Islanders, who have inhabited the islands since the early 19th century, are predominantly descendants of British settlers, and strongly favour British sovereignty. Neither state officially declared war, although both governments declared the islands a war zone.

A peace treaty is an agreement between two or more hostile parties, usually countries or governments, which formally ends a state of war between the parties. It is different from an armistice, which is an agreement to stop hostilities; a surrender, in which an army agrees to give up arms; or a ceasefire or truce, in which the parties may agree to temporarily or permanently stop fighting.

The need for a peace treaty in modern diplomacy arises from the fact that even when a war is actually over and fighting has ceased, the legal state of war is not automatically terminated upon the end of actual fighting and the belligerent parties are still legally defined as enemies. This is evident from the definition of a "state of war" as "a legal state created and ended by official declaration regardless of actual armed hostilities and usually characterized by operation of the rules of war". As a result, even when hostilities are over, a peace treaty is required for the former belligerents in order to reach an, agreement on all issues involved in transition to a legal state of peace. The art of negotiating a peace treaty in the modern era has been referred to by legal scholar Christine Bell as the lex pacificatoria, with a peace treaty potentially contributing to the legal framework governing the post conflict period, or jus post bellum.

The law of war is the part of international law that regulates the conditions for initiating war (jus ad bellum) and the conduct of hostilities (jus in bello). Laws of war define sovereignty and nationhood, states and territories, occupation, and other critical terms of law. Among other issues, the modern laws of war address the declarations of war; acceptance of surrender and the treatment of prisoners of war; the principles of distinction, as well as military necessity and proportionality; and the prohibition of certain weapons that cause unnecessary or excessive suffering.

The law of war is considered distinct from other bodies of law—such as the domestic law of a particular belligerent to a conflict—which may provide additional legal limits to the conduct or justification of war. The term law of war, or jus in bello, overlaps to some degree with opinio juris (also referred to as customary law), but refers to a very specific body of international law composed of customary and treaty-based law.

The Soviet invasion of Poland was a military conflict by the Soviet Union without a formal declaration of war. On 17 September 1939, the Soviet Union invaded Poland from the east, 16 days after Nazi Germany invaded Poland from the west. Subsequent military operations lasted for the following 20 days and ended on 6 October 1939 with the two-way division and annexation of the entire territory of the Second Polish Republic by Nazi Germany and the Soviet Union. This division is sometimes called the Fourth Partition of Poland. The Soviet (as well as German) invasion of Poland was indirectly indicated in the "secret protocol" of the Molotov–Ribbentrop Pact signed on 23 August 1939, which divided Poland into "spheres of influence" of the two powers. German and Soviet cooperation in the invasion of Poland has been described as co-belligerence.

The Red Army, which vastly outnumbered the Polish defenders, achieved its targets, encountering only limited resistance. Some 320,000 Poles were made prisoners of war. The campaign of mass persecution in the newly acquired areas began immediately. In November 1939 the Soviet government annexed the entire Polish territory under its control. Some 13.5 million Polish citizens who fell under the military occupation were made Soviet subjects following show elections conducted by the NKVD secret police in an atmosphere of terror, the results of which were used to legitimise the use of force. A Soviet campaign of political murders and other forms of repression, targeting Polish figures of authority such as military officers, police, and priests, began with a wave of arrests and summary executions. The Soviet NKVD sent hundreds of thousands of people from eastern Poland to Siberia and other remote parts of the Soviet Union in four major waves of deportation between 1939 and 1941.Soviet forces occupied eastern Poland until the summer of 1941 when Germany terminated its earlier pact with the Soviet Union and invaded the Soviet Union under the code name Operation Barbarossa. The area was under German occupation until the Red Army reconquered it in the summer of 1944. An agreement at the Yalta Conference permitted the Soviet Union to annex territories close to the Curzon Line (which almost coincided with all of their Molotov–Ribbentrop Pact portion of the Second Polish Republic), compensating the Polish People's Republic with the greater southern part of East Prussia and territories east of the Oder–Neisse line. The Soviet Union appended the annexed territories to the Ukrainian, Byelorussian and Lithuanian Soviet Socialist Republics.

The Sino-French or Franco-Chinese War, also known as the Tonkin War, was a limited conflict fought from August 1884 to April 1885 between the French Third Republic and the Qing dynasty for influence in Vietnam. There was no declaration of war.

The Qing armies performed better than in their other nineteenth-century wars. Although French forces emerged victorious from most engagements, the Qing scored noteworthy successes on land, notably forcing the French to hastily withdraw from occupied Lạng Sơn in the late stages of the war, thus gaining control of the town and its surroundings. However, a lack of foreign support, French naval supremacy, and northern threats posed by Russia and Japan forced the Qing to enter negotiations.