Abstract : Large-scale digital mergers, the consolidation of two or more enterprise technology estates following a corporate transaction, are among the most complex transformation programs in modern industry. Public post-mortem evidence consistently identifies the integration of Customer Relationship Management (CRM), Enterprise Resource Planning (ERP), Order Management, billing, and analytics platforms as the dominant source of value erosion, customer impact, and timeline slippage. This paper presents a framework-driven approach to enterprise system integration in such mergers and contrasts it with ad-hoc consolidation. It develops six architectural principles, characterizes five data-migration strategies with risk and duration trade-offs, specifies a six-layer testing program calibrated to merger scale, and reports operational and strategic outcomes drawn from comparative analyses of large-merger programs. Framework-driven integration reduces cutover incidents per billion transactions from 18.4 to 4.7, shortens synergy realization from 36–48 months to 18–24 months, and compresses integration cost from 12–18 percent of deal value to 6–9 percent. The findings argue that integration framework maturity is the dominant predictor of post-merger technology success and merits explicit due-diligence attention before transaction close.