In her (excellent) book Real Enemies: Conspiracy theories and American democracy, historian Kathryn Olmsted argues that Oswald's primary motivation was his desire to kill a prominent anti-communist. LHO had been committed to communism for quite some time, even during his time in the USMC. The FBI had been watching LHO for years and had concluded that he was a "violent, unstable sociopath prone to ideological extremism" [Olmsted, 114]. He had, however, become disillusioned with Soviet communism after his sojourn in Minsk from 1959 to 1962 and increasingly viewed Fidel Castro as the future of the ideology.

And as Olmsted notes, what's frequently left out of discussions around Oswald is his other assassination attempts. For example, earlier in 1963 he attempted (with the same rifle used in Dallas later that year) to kill Edwin A Walker, a retired general and extreme anti-communist. Oswald also wished to go to Cuba and (rather oddly) back to the USSR, but was stonewalled by Havana in his attempts to get a visa. At least part of his motivation for assassinating a noted anti-communist (JFK being in that category for LHO), was to 'prove' his ideological bona fides and commitment to 'the cause'.

I'd heartily recommend Olmsted's work on this. And the books is a great piece of work in general, and well worth reading. Michael Barkun, Joseph Ucsinski, Peter Knight, and Mark White have also done good work on the assassination and its surrounding context.

Hope this helps.

Malcolm