Mapping Critical Supply Chain Dependencies: A Sector-by-Sector Analysis of Single-Source Vulnerabilities in the United States and Major Trading Partners

Abstract

Existing single-sector risk frameworks systematically underestimate compound cascade risk because they cannot identify interactions among simultaneously stressed dependencies across sector boundaries. This paper introduces Mutual Threshold Saturation (MTS), a formal framework for compound supply chain vulnerability analysis that operationalises cross-sector dependency enumeration, identifies cascade pathways between sectors, and quantifies temporal exploitation windows — the lag between dependency identification and domestic capacity restoration. The framework is applied to seven critical sectors: pharmaceuticals and medical supply, critical minerals and semiconductors, fertilizer and agricultural inputs, energy and battery systems, telecommunications, domestic food supply concentration, and physical infrastructure.

Primary-source analysis underpins each sector. Analysis of the complete FDA Drug Master File database (Q4 2025, 40,397 records) finds that 75.3 per cent of all active pharmaceutical ingredients filed in the United States have a single registered source globally — 5,980 of 7,940 unique APIs — a finding that substantially exceeds prior secondary-source estimates. Applying consistent single-source and single-system criteria across all seven sectors yields 1,637 discrete enumerable dependencies, constituting a conservative floor figure.

The cross-sector integration reveals five findings that are invisible to single-sector analysis: (1) processing chokepoints are more strategically significant than extraction chokepoints in every sector examined; (2) supply chain opacity is itself a structural vulnerability independent of any individual dependency; (3) domestic regulatory architecture generates category-distinct dependency types requiring different mitigation instruments; (4) mitigation strategies systematically reshape rather than eliminate the compound vulnerability landscape; and (5) the compound synthesis asymmetry — in which adversary strategic planning has likely assembled a more comprehensive dependency map than any U.S. government agency holds — constitutes a meta-level vulnerability. The Hormuz crisis event of February–March 2026 provides real-time validation of the MTS cascade model: simultaneous disruption to oil, fertiliser, LNG, and agricultural inputs through a single geographic chokepoint reproduced exactly the cross-sector cascade structure the framework predicts, across institutional response silos with no unified coordination mechanism.

The MTS framework implies three policy instruments calibrated to the compound risk structure: a unified cross-sector vulnerability assessment mandate, ingredient- and component-level supply chain disclosure requirements, and strategic reserve architecture spanning all critical sectors rather than petroleum alone. These represent necessary but not sufficient conditions for managing the MTS equilibrium before its conditional stability degrades further.

Keywords: supply chain vulnerability, compound dependencies, mutual threshold saturation, defence economics

JEL Classification: F21, H56, L14, Q37