Coalition Politics: Why German Governments Are Always Compromises

A German Chancellor needs the confidence of a majority of the Bundestag to take office (Art. 63 GG). On paper this is simple. In practice it has been hard for decades, because no single party has won an absolute Bundestag seat majority since 1957, when the CDU/CSU under Konrad Adenauer won 50.2 % of the Zweitstimmen — which in that pre-5%-threshold era with fewer parties translated into a bare absolute seat majority of 270 of 519 seats. Since 1957, no single party has won an outright Bundestag seat majority, and federal governments have in each case been formed as coalitions (or, briefly, as minority-caretaker arrangements pending a new coalition). Understanding why starts with the arithmetic.

Recent election results (Zweitstimme shares, Bundestag seat shares).

• 2017: CDU/CSU 32.9 % (246 seats), SPD 20.5 % (153), AfD 12.6 % (94), FDP 10.7 % (80), Linke 9.2 % (69), Grüne 8.9 % (67). Bundestag total 709.
• 2021: SPD 25.7 % (206), CDU/CSU 24.1 % (197), Grüne 14.8 % (118), FDP 11.5 % (92), AfD 10.3 % (83), Linke 4.9 % (39 via Grundmandatsklausel), SSW 0.1 % (1). Bundestag total 736.
• 2025 (official final result, Bundeswahlleiterin Mitteilung 29/25, 14 March 2025): CDU/CSU 28.6 % (208 seats), AfD 20.8 % (152), SPD 16.4 % (120), Grüne 11.6 % (85), Linke 8.8 % (64), SSW 0.2 % (1). BSW 4.97 % (0 seats — missed the 5 % threshold, no direct constitüncies). FDP 4.3 % (0 seats). Bundestag total: 630.

From these numbers, the coalition arithmetic for 2025 is:

• A simple majority requires 316 seats out of 630.
• CDU/CSU alone (208) — far short.
• CDU/CSU + SPD (208 + 120 = 328) — viable and the arithmetically smallest two-party majority.
• CDU/CSU + Grüne (208 + 85 = 293) — short.
• CDU/CSU + AfD (208 + 152 = 360) — arithmetically a majority, but politically excluded by CDU/CSU's own resolution (Unvereinbarkeitsbeschluss, confirmed by CDU federal conference May 2024).
• SPD + Grüne + Linke (120 + 85 + 64 = 269) — short.

In other words, in the 2025 Bundestag, only a CDU/CSU-led coalition with the SPD has both the numbers and the political acceptability to govern. The resulting negotiations began in late February 2025 and produced a coalition agreement signed in April 2025; Friedrich Merz was elected Federal Chancellor by the Bundestag on 6 May 2025 (Art. 63 GG; Bundestag Plenarprotokoll 21/5, 6 May 2025).

Why is fragmentation increasing? Several trends overlap:

1. The combined vote share of the two historically dominant Volksparteien (CDU/CSU and SPD) has dropped from ~85 % in the 1970s to ~45 % in 2025.
2. New parties have entered the system (Greens since 1983, PDS/Linke since 1990, AfD since 2017, BSW in 2025).
3. Regional and social-value cleavages have become more salient than the classic economic left-right divide. The political compass axes have effectively expanded.

Why are three-party coalitions becoming more common? When two-party combinations do not reach 50 %, three are needed. The 2021–2024 Ampel (SPD, Greens, FDP) was the first three-party federal coalition since 1957. By 2025 the numbers allowed a return to a two-party coalition only because the CDU/CSU's share rebounded and the FDP left the Bundestag.

Coalition mathematics matters for voters as well. A vote for a small party can be decisive if that party clears 5 %; the same vote is wasted if the party misses the threshold. In 2025 voters who wanted the FDP in government instead removed it from the Bundestag entirely by failing to deliver 5 %. This is the hard mathematical reality behind the tactical consideration known as Nützlichkeitswahl — voting strategically rather than expressively.

Sources: Die Bundeswahlleiterin, Endgültige Ergebnisse Bundestagswahlen 2017, 2021, 2025 (bundeswahlleiterin.de). Deutscher Bundestag, Sitzverteilung im Bundestag 2021 und 2025 (bundestag.de). BpB, Parteien, Koalitionen und Regierungsbildung (bpb.de, 2025). Niedermayer, Bundestagswahl 2025: Parteien und Wahlverhalten, Zeitschrift für Parlamentsfragen 2/2025.