The Poles, officially numbering 507,000 in 1931, had been second only to the Italians as the largest foreign nationality in France since the mid 1920s. But at the time of the following census, carried out in 1936, their numbers were placed at only 423,000, although they retained their overall rank. Naturalisations, albeit very few, a slight decline in the birth rate and an increase in the death rate partially account for this drop in numbers. Departures from the territory make up the rest.

Every immigration has its share of returns. Disappointment, failure to adapt to the new conditions of life and work had led to departures in the 1920s, even in the very first months, which entailed a breach of the work contract binding the worker to his employer for a year. Over the next decade, this form of headlong departure tended to disappear, because the crisis had dried up recruitment and most of the Poles in France were no longer newcomers. But there were still voluntary departures for personal reasons, such as those of single men desiring to rejoin their aged/ailing parents or who had accumulated sufficient savings to buy a plot of land which would protect them from starvation. Those cases took the train back to Poland, paying their own tickets and the additional expenses for the transport of baggage and furniture.

However, the involuntary departures tended to prevail, and their numbers increased. There were, on the one hand, as in the 1920s, individuals deported in accordance with the law of December 1849 :  "vagabonds" (meaning foreigners without papers, notably the identity card which they were required to have since 1917), those involved in drunken brawls, men accused of political activities, most often union activists (while unionism as such was not punishable because the Waldeck-Rousseau Law allowed foreign workers to join unions). To cite only two examples, both dating from 1934 :  the deportation of Thomas Olszanski, Communist and union leader denaturalised two years earlier, and that of 77 miners from Leforest (Compagnie de L'Escarpelle in the Pas-de-Calais department), who led a strike in the bottom of the mine. The departures which were by far the most numerous and typical of a period of under-employment consisted of the repatriation of entire families. In 1934-1935, the Houillères du Nord mining company organised the convoys themselves--the free (but obligatory) train, 30 kilograms of luggage per person (which prevented taking everything along), and a rapid departure within two days after dismissal.

Where do the responsibilities lie? In spite of appearances, more on the side of the government than that of management, because the employers were hoping for a recovery and knew that they could not do without skilled miners.