  We prove that if $X$ is a subspace of $L_p$ $(2<p<\infty)$, then either $X$
embeds isomorphically into $\ell_p \oplus \ell_2$ or $X$ contains a subspace
$Y,$ which is isomorphic to $\ell_p(\ell_2)$. We also give an intrinsic
characterization of when $X$ embeds into $\ell_p \oplus \ell_2$ in terms of
weakly null trees in $X$ or, equivalently, in terms of the "infinite asymptotic
game" played in $X$. This solves problems concerning small subspaces of $L_p$
originating in the 1970's. The techniques used were developed over several
decades, the most recent being that of weakly null trees developed in the
2000's.
