It is hard to identify attempts to alleviate class conflct as most of what was going on consisted of attempts to win the class conflict, not to alleviate it. Labor unions, for example, were not really trying to alleviate class conflict but to win it for the workers.
You might argue that the progressive movement was an attempt to alleviate class conflict. In that movement, members of the middle class tried to reduce the tensions between the rich and the poor. They did so by trying to take power from the rich and to prevent the rich from hurting the poor. They also tried to bring the poor up into the middle class. By doing so, you can argue, they were trying to reduce the amount of class conflict.