How does trade impact the comovement of output across countries? I provide analytical expressions for the second moments of real GDP in the two most common frameworks of International Trade while allowing for an arbitrary number of countries, sectors, and input-output linkages. In a stylized economy, I show how differences in the bilateral elements of the influence matrix converge linearly to zero as the number of sectors and countries increases, that the extensive margin of trade does not guarantee a higher correlation of real output across countries, and that quantitative predictions hinge on assumptions about deep parameters. I calibrate the models using world input-output data and data on exporting firms and compute the correlations of real value added across 44 countries and 56 sectors. I find that Old Trade under-predicts the correlation of GDP in the data by an order of magnitude, while the New Trade Model with monopolistic competition and heterogeneous firms predicts correlations between one-fifth and one-half of those observed in the data, but that result hinges on how parameters are calibrated in light of each model.