I work at the intersection of international relations, comparative politics, and social science methods. My research has two complementary strands. The substantive strand examines the domestic politics and political contestation of international security: why democracies differ in their involvement in military operations and their stance on military assistance, how parliaments and political parties shape decisions on the use of force, and how foreign policy changes under geopolitical transformation, most recently in work on Germany’s Zeitenwende and European responses to Russia’s war against Ukraine. The methodological strand focuses on Qualitative Comparative Analysis (QCA) as a set-theoretic method for descriptive and causal inference. I am also working on multi-method research design, especially on combining QCA and process tracing for cross-case and within-case inference.
International Security • QCA • Current Work • Funded Projects and Consultancy
The Domestic Politics of International Security
This research strand began with my dissertation on democracies’ participation in the conflicts in Kosovo, Afghanistan, and Iraq, published as Democratic Participation in Armed Conflict (Palgrave Macmillan, 2014). The book received the Best Dissertation Award of the German Political Science Association (DVPW). From there I focused further on parliamentary war powers, with an article on the British House of Commons and the conflicts in Libya and Syria (West European Politics, 2017) and the special issue “Parliaments in Security Policy” (British Journal of Politics and International Relations, 2018), which I edited with Dirk Peters on the basis of a workshop funded by the German Foundation for Peace Research. The House of Commons article was later cited in the 2019 report of the Dutch Expert Group on Political Support for Interstate Use of Force and Humanitarian Intervention, convened by the Minister of Foreign Affairs. A related set of studies concerns democracies’ involvement in multinational military operations: the conditions under which democracies withdraw from coalitions (European Journal of International Security, 2020), European involvement in the coalition against Daesh (European Political Science Review, 2022), and a conceptual framework for national restrictions in the special forum I edited with Stephen Saideman for Contemporary Security Policy (2019).
Since joining VU Amsterdam in 2022, I have focused this research strand on European responses to Russia’s war against Ukraine. Articles in Politics and Governance (2024) and the Cambridge Review of International Affairs (2025) examine Germany’s Zeitenwende and the party politics of national role contestation under the “traffic light” coalition. Chapters on the German National Security Strategy (2025) and on the implementation of the Zeitenwende (2026, in press) continue this work. Within the VU Starter Grant project NEST – Navigating the Storm (2023–2027, PI Chendi Wang), I lead the work package on the Russia–Ukraine war and the political contestation of foreign policy, together with Wolfgang Wagner, and co-designed the project’s YouGov survey on public attitudes toward support for Ukraine. I also co-supervise Richard Sonneveld’s PhD on the party-political contestation of foreign policy in the Netherlands, together with Wolfgang Wagner and Michal Onderco (Erasmus University Rotterdam).
Qualitative Comparative Analysis
My methodological research strand focuses on QCA as a set-theoretic approach to descriptive and causal inference. Qualitative Comparative Analysis: An Introduction to Research Design and Application (Georgetown University Press, 2021) takes readers from research design through calibration and analysis to the interpretation of their results. It also provides background on theories of causation and the critical debate on QCA. The Japanese translation appeared with Chikura Publishing in 2023. The book is accompanied by the R Manual for QCA, which I update regularly, and by replication materials on Harvard Dataverse. Related work includes a review of QCA in international relations (International Studies Review, 2022, with Tobias Ide) and the chapter on QCA in foreign policy analysis in the Routledge Handbook of Foreign Policy Analysis Methods (2023), which I edited with Falk Ostermann. I also use the method in applied studies, for instance on the unintended consequences of UN sanctions (Contemporary Security Policy, 2022, with Katharina Meissner), on agency slack in international bureaucracies in the DFG project described below, and recently on adaptability among public sector organizations (Public Policy and Administration, 2026, with colleagues at Sant’Anna School of Advanced Studies).
Teaching QCA is an integral part of this research strand. Since 2016 I have taught the QCA course at the Summer School in Social Sciences Methods in Lugano, and I give workshops at universities and public institutions, recently at Utrecht University School of Governance, Jagiellonian University in Kraków, and for the evaluation staff of the UK Foreign, Commonwealth & Development Office. Since 2025 I have advised an NIH-funded study at the University of Pennsylvania’s Perelman School of Medicine on integrating QCA into a multi-method design. I am a founding member of the Methods Excellence Network (MethodsNET) and serve on the advisory board of COMPASSS.
Current Work
Two book projects occupy most of my current methodological work. A second edition of Qualitative Comparative Analysis is under contract with Georgetown University Press. With Hilde van Meegdenburg (Leiden University), I am preparing a book manuscript combining QCA and process tracing in multi-method research, provisionally titled Uncovering Causal Symptoms, which sets out how to combine set-theoretic cross-case analysis with within-case process tracing. We presented the manuscript in June 2026 at the Advances in Qualitative and Multi-Method Research (AQMMR) workshop, held virtually as part of the Institute for Qualitative and Multi-Method Research (IQMR) at Syracuse University. The book manuscript was also the subject of my keynote at the QCA Conference of the Americas in Cincinnati in March 2026.
On the substantive side, my current work concerns the party-political and public contestation of European security policy since the Russian full-scale invasion of Ukraine in 2022, drawing on the YouGov survey data we gathered for the NEST project (work with VU colleagues Wolfgang Wagner, Ben Crum, and Chendi Wang). Among other aims, the NEST project seeks to examine how European respondents position themselves on questions of military assistance, what their political preferences are, and what this means for the foreign policy space in European democracies. Beyond this, I am working on a chapter on “Political Parties in Foreign Policy” for a new Handbook of Foreign Policy Analysis edited by Marijke Breuning (University of North Texas) and Leslie Wehner (University of Bath).