“When Paris Went Dark: The City of Light Under German Occupation, 1940-1944” by Ronald C. Rosbottom. Little, Brown and Co., 2014. $28.

In May 1940, when the German Blitzkrieg broke through France’s Ardennes region, the defense of Paris became impossible. Both sides quickly agreed to consider the French capital an open city: the French to prevent its destruction, the Germans to present a “civilized face” in Western Europe.

Indeed, Adolf Hitler regarded Paris as the model for his planned reconstruction of Berlin. Thus began German rule lasting some 50 months, slightly more than 1,500 days. Ronald Rosbottom, a distinguished scholar at Amherst College, recounts life in Paris during the Occupation and asks “which actions, exactly, constitute collaboration and which constitute resistance?”

At the outset, the Germans offered soothing words: little would change except for political opponents and Jews. Yet immediately, they restricted movement, imposed curfews, limited nourishment and changed the clocks to Berlin time.

The ration for adults was 1,200 calories a day, less than half of normal — and three of the four winters were among the coldest of the century. For most Parisians, life was difficult, shabby, dirty, hungry and cold. They might get by (se débrouiller), but “the war ... scratched away at the veneer of decorum, so important to a society’s stability.”

For Parisian Jews, whether French for generations or recent immigrants, life was dangerous, even lethal. Their houses and apartments were seized and their businesses “Aryanized” — turned over to Germans or their sympathizers. They had to wear a yellow star on their clothing, in effect, “a mobile ghetto.” They could expect no sympathy from the Paris Police, who followed German orders to carry out the Grand Rafle on July 16-17, 1942, arresting more than 13,000 Jews, among them more than 4,000 children, and holding them in squalor at the Vélodrome d’Hiver (an indoor bicycle racing track near the Eiffel Tower) for transport to the concentration camps of Eastern Europe.

Some Parisians collaborated, at times openly, with the Occupation, anticipating better treatment and expecting Germany to win the war. Others resisted through underground publications, sabotage and assassination. Most kept their heads down, obeying when they thought they had no choice, disobeying when they thought they could do so.

Once the Germans decreed the yellow star, a school principal called all the students together and warned that he would refuse to recommend anyone who bullied a Jewish boy.

At the Lycée Rollin, a secondary school in the Montmartre district, the German language teacher, Daniel Decourdemanche, led an especially daring resistance group until his capture and execution. After the war, the school became the Lycée Jacques Decour, his nom de guerre.

When the Free French 2nd Armored Division under Gen. Philippe Leclerc — wearing American uniforms and using American tanks — liberated Paris on Aug. 25, 1945, collaborators and sometime collaborators faced a reckoning.

Mock judicial proceedings led to back-alley shooting of the men and to public shaming, usually through shaving their heads, of the women. Soon enough, however, the leader of the Free French, Gen. Charles de Gaulle, imposed traditional judicial procedure on this settling of scores.

Discreetly, but repeatedly, Rosbottom reminds how difficult each daily decision, how charged each encounter with the authorities, could be. No, Paris never suffered anything approaching the starvation and misery of Leningrad or the annihilation of Warsaw.

But anyone who condemns every French man or woman who sought an accommodation with the Germans should recall that judgment about collaboration and resistance is deceptively easy after the fact and at a distance. Take note of pertinent periods in our own history.

Benjamin Franklin Martin is the Price Professor of History at Louisiana State University. His most recent book is “Years of Plenty, Years of Want: France and the Legacy of the Great War” (2013).