Spain's socialist government under Prime Minister Pedro Sánchez has enacted a royal decree to legalize approximately 500,000 to 840,000 undocumented migrants, effective from mid-April 2026 with applications open until June 30. Official estimates center on 500,000, though independent analyses and police unions project higher figures as migrants line up at consulates and municipalities for documentation. The measure, the seventh regularization in four decades totaling over 1.75 million permits historically, grants one-year renewable residence and work permits to those proving five months of continuous residence before January 1, 2026, and a clean criminal record. Sánchez has framed it as both moral justice—recognizing migrants already integrated into daily life, workplaces, and churches—and economic necessity for an aging nation facing severe labor shortages in agriculture, caregiving, and services. This aligns with Spain's fertility rate hovering at 1.1-1.2 children per woman (1.07 among natives), negative natural population growth for nearly a decade, and a foreign-born population now exceeding 20% of the total, driving all recent population gains toward 50 million. Critics, including the center-right PP and far-right Vox, decry the use of a royal decree to bypass parliament as executive overreach, arguing it rewards illegality, incentivizes further arrivals (particularly from Morocco and Latin America), and accelerates 'thirdworldization' of public services, housing, and social cohesion. Legal pushback has materialized swiftly: the conservative group Hazte Oír secured Supreme Court acceptance of its challenge, requiring the government to produce its full administrative file within 20 days. While the Court declined an immediate precautionary suspension—allowing processing to continue—the case highlights core tensions between bureaucratic expediency and constitutional safeguards requiring parliamentary approval for sweeping policy changes. Deeper analysis reveals this as more than routine policy. Spain's repeated amnesties create a predictable cycle that entrenches high net migration as the sole counter to native demographic collapse, with old-age dependency ratios projected to worsen dramatically (from 2.6 to 1.2 workers per retiree by 2050). Legalized migrants gain EU free-movement rights, positioning Spain as a de facto gateway that impacts the entire Schengen area at a time when neighbors like France, the UK, and Italy tighten borders. Integration data underscores risks: foreigners face higher poverty (47.8% for non-EU), overcrowded housing, educational gaps, and concentration in low-skill jobs, potentially compounding strains on healthcare and welfare already evident in urban centers. Vox's warnings and regional electoral shifts signal rising populist backlash. This episode crystallizes Europe's crossroads—short-term fiscal and labor pragmatism versus long-term cultural and political transformation that may prove irreversible once citizenship pathways open after years of residency. The Supreme Court review, though unlikely to fully unwind grants already issued, may constrain future decree-based expansions and force greater legislative accountability.