Between 1740 and 1848, an overwhelming majority of the British ruling class determined that a legislative union with Ireland was preferable to the devolved constitutional framework of the eighteenth century, succeeded in securing the enactment of such a union, and resolved upon an uncompromising defense of the new constitutional arrangement when it became the focus of Catholic nationalist discontent. This book explains how the British ruling class came to support a union with Ireland, and why the British elite insisted upon upholding the union after it became evident that the measure had failed to solve the basic problems of Irish governance. It also explicates the various strategies adopted by successive British governments for maintaining the union in response to the strident, if sporadic, opposition to the constitutional settlement offered by Irish nationalists from 1830 to 1848. The Making of British Unionism provides an important reassessment of the British-Irish relationship in the late eighteenth and early nineteenth centuries.