Jewish solidarity is essentially described by scholars as the impulse that is acted upon by Jews to come to the aid of or to reach out with help to other Jews who are suffering hardships in other communities (Rabbi Berel Wein). I.J. Singer's book The Brothers Ashkenazi portrays the story of two rival brothers, twins, during a political era that ends in random violent turbulence aimed as a pogrom at the Jews of Lodz. Political futility reigns as Simcha Meir ("Max") learns that wealth and power cannot protect him against anti-Semitic violence.
Whether Singer means to point to a state of political futility for Jewish solidarity is a question worth debate, since he ends the story with Jacob rescuing his brother; the brothers then reconcile and overcome their past enmity. Yet, when they attempt to reenter Poland together, Jacob refuses to repudiate his Jewish religion and is killed for it, while Max, encouraged by the Polish guards, does reject his religion.
It is true, therefore, that the novel seems to depict a state of futility for Jewish solidarity: Jewish sons turn against fathers; Jewish sons turn against other Jewish sons (i.e., Nissan and Simha Meir); Jewish communities turn against other Jewish communities (e.g., Lodz Jews and Litvaks). It may be that Singer intends to present a portrayal of politics in a state of futility for human solidarity, as Rebecca Newberger Goldstein explains in "Love, Tough and Not Tough":
It is not religious backwardness or economic conditions or political theories that are ultimately to blame. It is human nature itself that damns us, in I. J. Singer’s eyes. The possibility that Nissan can only glance at in his utter despair—the corruption mixed with human nature—is Israel Joshua’s conclusion. (Goldstein)
[Nissan]: "Maybe man was essentially evil. Maybe it wasn't the fault of economic circumstances, as he had been taught, but the deficiencies of human character." (The Brothers Ashkenazi)
Simha Meir, in particular, drawing from inexhaustible reserves of ingenuity and drive, serves only to demonstrate, by the very indefatigability of his exertions, the awful fatality and futility of human efforts in a world so thoroughly deformed by injustice... (Goldstein)