Poland was the first country to be occupied by the Nazis during the second world war and one of the last to be liberated, with the final expulsion of German forces coming only in February 1945. In this comprehensive survey, Halik Kochanski aims to avoid the pitfalls of Polish-nationalist historiography and deliver an impartial account of this terrible period in Polish history. She does not wish, she says, to engage in "competitive victimhood" though this does not prevent her publishers from claiming "the fate of the inhabitants of Poland was the most terrible of any group in the second world war" (most historians reckon the fate of the inhabitants of Belarus was worse).

This book aims to tell the story of all the Poles during the war, so it gives due prominence to those who spent most of these years outside Poland. The fate of the Poles deported to remote parts of Siberia and Kazakhstan by the Soviets after their occupation of eastern Poland in September 1939  according to recent estimates around 300,000  was a grim one. Dumped in labour camps or impoverished rural settlements, they were forced to work on meagre rations, and perished in large numbers from sickness and malnutrition.

Vivid interviews with survivors reveal what they did to stay alive: they used their higher level of education to get better jobs; bribed and bartered their way to safety; stole sheep to eat; begged. Many did not survive: the Soviet secret police shot tens of thousands of prisoners of war captured during their invasion, including more than 14,000 Polish officers in the forest of Katyn. To the Soviets, these were the embodiment of Polish nationalism, a force that had to be exterminated in the interests of communism.

Things began to change when Germany invaded the Soviet Union on 22 June 1941. Churchill demanded the release of Polish prisoners of war in Soviet camps, and soon they were streaming into recruiting centres, "exhausted", as one witness reported, "in rags, impoverished, covered with sores, louse-infested, without hair  resembling rather some strange creatures more than human beings". By March 1942 there were 70,000 Polish men under arms in the Soviet Union. By agreement with the British, they were sent to the Middle East along with thousands of Polish civilians, to bolster defences against Rommel's threatened invasion. Subsequently, many found their way to Britain to join the allied forces there; some were even sent to India.

Those who stayed behind in occupied Poland had to suffer what Kochanski rightly calls a "reign of terror" in the Soviet-  occupied east of the country, where the majority Ukrainian and Belarusian population were treated as workers and peasants, while the Poles  many of them landowners  were persecuted as bourgeois and aristocrats. The Bolshevik revolution was imposed by force of arms, and all the inhabitants of the area were enrolled as Soviet citizens. The economy collapsed, and tens of thousands of Jews who had fled the German invasion in the west and welcomed the Soviet invasion now begged to be allowed to return.

Encouraged by the Soviets, Ukrainian nationalists robbed and murdered Poles, killing around 600 and pillaging numerous houses and estates. But they were brought under control after they had done the job; their leaders were sent to Siberia, and their movement suppressed. As a result, Ukrainian nationalism swung behind the Germans, and its supporters provided the personnel for the extermination camps and engaged in massacres and attacks on Jews in the areas controlled by the Germans.

Later, as the Germans retreated, a civil war broke out between armed bands of Poles and Ukrainians. The Polish state recreated at the end of the war forcibly expelled around half a million Ukrainians to the east  many of whom had been settled in Poland for generations  killing 4,000 in the process. Meanwhile, 1.5 million Poles were "repatriated" to the new state from Ukraine, Belarus and other areas to the east, some with financial inducements, others by force. Kochanski does her best to see both sides of the picture, but relies too much on interviews with Polish survivors  and the generally well-sustained impartiality of this book slips a little when she accuses Ukrainians of "disloyalty to the Polish state".

In western and central Poland, the rule of the Nazi occupying forces was brutal in a different way. Classified as subhumans, Poles were expropriated, transported to Germany for forced labour, starved, arrested, and killed in their thousands. Many were enrolled (often against their will) in an official list of ethnic Germans. Around 200,000 supposedly "Germanic" children were kidnapped and sent to Germany to be adopted by childless couples and given a new identity; fewer than a fifth managed to return after the war. Even the SS conceded that "such oppression as is being borne by the Polish people has never been borne by any other nation." The records of a single prison in Warsaw show 100,000 Poles were interrogated there between October 1939 and July 1944, of whom 60,000 were sent to concentration camps and 17,000 executed. One prisoner, arrested because he had given medical treatment to Jews in a nearby ghetto, described what went on there as "an orgy of sadism and unspeakable cruelty, cynically planned and executed".

The fate suffered by Polish citizens of Jewish ethnicity was worst of all. Around 90% did not survive the war. Herded into overcrowded and insanitary ghettos, hundreds of thousands succumbed to starvation or disease before the rest were shipped off to extermination camps in various parts of occupied Poland. Some Poles helped conceal Jews as best they could, for a variety of motives, others betrayed them; a few joined in the persecution. The Polish underground home army provided the Warsaw Ghetto insurgents with a handful of arms but, Kochanski argues, lacked the resources to do any more.

Kochanski's touch here is less sure than it is on the sections on the Soviet occupation: she confuses the "hunger plan" devised to supply German armed forces by starving Slavs and Jews, with the "general plan" for the east, a far more ambitious, long-term scheme to kill 30-45 million Slavs and populate eastern Europe with ethnic Germans. And she misunderstands the purpose of the grisly medical experimentation carried out on Polish women in the Ravensbrück concentration camp by Professor Karl Gebhart, who did not "remove leg bones, to be used for wounded German soldiers"  transplants were not possible at the time  but smashed the bones to simulate war wounds, infected them, and tested his favourite remedy on them  sulphonamide, a drug that had no discernible effect.

Part of the problem here is that Kochanski makes no use at all of the voluminous German literature on the Holocaust, on medical experimentation, and the occupation of Poland; and indeed she makes surprisingly little use of sources in Polish. Apart from the interview material, her book is almost entirely based on English-language documents and secondary literature. This undermines her claim that the events she describes are "largely unknown" in the English-speaking world. Nevertheless, this is a comprehensive study that provides a fair-minded introduction to the subject.

 Richard J Evans's The Third Reich at War is published by Penguin.