A new proof of James' sup theorem

We provide a new proof of James’ sup theorem for (non necessarily separable) Banach spaces. One of the ingredients is the following generalization of a theorem of Hagler and Johnson (1977) : “If a normed space $E$ does not contain any asymptotically isometric copy of ${\mathrm{\ell }}^1(\text{IN})$, then every bounded sequence of $E^{\mathrm{\prime }}$ has a normalized block sequence pointwise converging to 0”.