I suggest the following article/chapter from "Dissecting the Holocaust" (2019 version):
In the Second World War, the practice of taking and killing hostages was continued by all parties involved. The fact that it occurred frequently on the German side may be partially explained by the great extent of the enemy territory occupied by fairly weak military forces, but also by the fanatical resistance of the population of these occupied regions, who paid no heed to the relevant regulations of the Hague Land Warfare Convention of 1907.
Since the attitude of the civilians towards the German soldiers was more positive in Italy than in the other European countries, few executions of hostages and reprisal prisoners took place there, apart from the special incident of the “Fosse Ardeatine” (March 24, 1944).
Between 1941 and 1944 executions were especially numerous in the Balkans, where partisan activities were particularly widespread. In this respect, the Chief of the Wehrmacht Supreme Command issued an order on September 16, 1941, which named the vengeance death of 50 to 100 Communists per German soldier as generally appropriate ratio.2297 On the basis of this order, an attack of bandits at Topola (resulting in 22 dead and 16 missing on the German side) was followed by the order to execute 2,200 prisoners; 449 were in fact executed.2298 There were also numerous other instances of hostage killing, but the ratio of 1:100 was never applied.
The war in Russia also led to reprisals. Paget,2299 for example, reports that 50 hostages were shot in Simferopol in the Crimea, after executions at a ratio of 1:100 had been threatened as vengeance against bomb explosions where Germans were killed.
In the Belgian trial of General von Falkenhausen, the conditions in Belgium and northern France were discussed in detail. In particular, an extensive collection of documents was presented, which Behling has supplemented with a chronological table of the executions.2300
This was a case of numerous attacks by partisans. Reprisal executions followed in each case; the ratio of victims of the attacks to hostages executed varied from 1:5 to 1:25. Generally, 10 Belgians or French were shot per German killed.2301 The number depended on the circumstances of each particular case, for example on the severity of the attack.
In one case, after a German soldier was murdered in Haarlem, Holland, the execution of 100 prisoners was ordered; 10 were actually shot.2302
There is no need to go into details here, since the German side always took pains to establish the permissibility of reprisals and reprisal killings. Examples from the opposing sides, on the other hand, are more impressive. The aforementioned collection of documents from the Falkenhausen Trial contains extensive materials on this topic.2303 We shall just mention the following example.
After the capture of Bengasi, Montgomery stated that he believed that numerous mines and traps had been set in the city. For every British soldier that was killed, he would have 10 Italians shot.2304 A November 30, 1944, radio message from the Allied headquarters in Paris stated:2305
“Regarding General Leclerq’s proclamation in Strassbourg, according to which 5 hostages were to be shot for every French soldier killed in ambush, Headquarters has ordered that Allied expedition troops operate in accordance with the Geneva Convention of 1929 and especially its Article 2, which states that reprisals against prisoners of war are prohibited.
Under martial law, however, taking hostages in order to ensure that the inhabitants of the occupied territory obey the orders of the military government is permitted by the laws of warfare. Such hostages may be tried in court, and even sentenced to death.
Therefore, under certain circumstances – especially in cases where civilians have violated the orders of the Geneva Convention – the threat expressed by General Leclerq may be enforced, but not against prisoners of war.”
According to Falkenhausen Document 58a, 6 officers and 34 soldiers were executed at Annecy (Haute Savoie), and another 40 Germans at Habère, as reprisal for atrocities allegedly committed by a Russian battalion.
On April 24, 1945, in Reutlingen, Württemberg, four reprisal prisoners were shot by the French for the murder of a French soldier.2306 On April 28, 1945, the following announcement was made in Leutkirchen:2307
“[…] 4. If a German shoots at Frenchmen, or if any other incident whatsoever happens, 5 houses will be torched and 100 Germans executed.
[…] 6. I am responsible, on pain of my own death, to ensure that these orders are enforced […] the Mayor […]”
In Markdorf, 4 German civilians were executed per 1 French soldier shot.2308
In Saulgau it was proclaimed on April 27, 1945, that if a French soldier were killed or even only wounded, 20 hostages would be shot and the corresponding city district would be burned to the ground.2309
The Berlin Ordinance of July 1, 1945,2310 stated, inter alia:
“Anyone who commits an attack on a member of the occupation forces or on a bearer of official functions, or who commits arson for reasons of political enmity, seals not only his own fate but that of 50 former members of the Nazi Party as well. Their lives are forfeit together with that of the assassin or arsonist.”
Falkenhausen Document 74 tells of the execution of 8-12 Germans for one officer killed during the American march-in in Treseburg.
Further threats of reprisal killings were proven in the SouthEast Trial in Nuremberg in Case VII;2311 examples include a ratio of 1:25 in Stuttgart, 1:10 in Birkenfeld, 1:30 in Markdorf, and an American threat of 1:200 in Harz. Hoppe2312 mentions further that the Americans took French officials hostage in 1941 in Syria; as well, the Russians took Persian officers hostage in 1949 in Azerbaijan. Further, the French took and killed hostages in Indochina.2313 Sonnenburg2314 reports that the French shot 80 prisoners of war in Fort Mont Lucon in 1944, as well as 20 hostages in Saigon in May 1951.
According to the publication Der Heimkehrer,2315 French officers and soldiers returning from Indochina stated that they could not understand what was happening at that time, 7½ years after the war, to the former members of the German occupation forces. They pointed out that incidents like Oradour take place in Indochina on a weekly basis, and must take place, in fact, for the sake of the protection of the French troops there.
As we can see, hostages were taken by all sides in World War Two, and in many cases they were also killed as reprisal.
Given that the Germans lost the war and were subsequently subjected to various "War crimes" show trials - unlike the "Allies" - attempts to investigate atrocities by the "Allies" were diminutive in comparison.
Heck, the US government even helped their "Gallant Soviet ally" by hushing up their mass murder of the Polish elite at the Katyn forest: