Throughout the novel, we see several conflicts between different social classes unfolding.
The most important conflict is between old money and new money, made physical in the difference between East Egg (where the traditional aristocrats tend to live) and West Egg (which features the newly rich, Gatsby being the most prominent example).
We see this conflict most strongly when the Buchanans attend one of Gatsby’s famous parties and are shocked to witness what they view as the coarse manners of his guests. A lesser example is also seen when Gatsby accepts an invitation to a gathering of ‘old money’ aristocrats, unaware that it was not seriously intended because he is not used to communicating with that class of people (pp. 99-100).
The more general conflict between lower and upper classes is also featured, mostly exemplified in Tom’s conversations with George Wilson (p. 27, 118). Tom clearly shows his upper class dominance in these encounters, while Wilson has to endure his rudeness because he is desperate for the economic benefits that Tom might provide if he can secure a deal with him. Tom seems to enjoy delaying the deal and toying with George’s emotions - and at the same time he even has an affair with George’s wife, which further shows his power and control in the situation.
We also see the contrast between upper and lower classes in the stark difference between the colourful, vibrant parties at Gatsby’s and the lifeless, gray wasteland of the valley of ashes.