# Sinusoidal History > Eight historical cycle theories overlaid on one shared time axis (1600–2050), each paired with a real long-run empirical data series. A comparison tool — not prophecy. The site is at https://sinusoidal-history.skylarkcreations.com. Source code is at https://github.com/u00dxk2/sinusoidal-history. Built by David Kooi at Skylark Creations, April 2026, after a phone-call conversation with Mark R about whether you could plot Khaldun, Kondratiev, Huntington, Perez, Turchin, Dalio, and Strauss-Howe as actual sine waves on one axis and see where they net out. Schlesinger Jr.'s ~30-year liberal/conservative cycle was added in a second pass, also at Mark's suggestion. The eight cycles, by ascending period: Schlesinger Jr. (30y), Kondratiev (54y), Perez (55y), Huntington (60y), Dalio (75y), Strauss-Howe (84y), Khaldun (120y), Turchin (150y). Seven of eight are paired with a real long-run data series; Perez has no paired data this round. Headline editorial point: most of the cycles peak near the present, but that is a *selection effect*, not convergence — theorists writing today anchor their forecasts to the world they live in, and we read them precisely because their climaxes land in our era. The site says this on the home page, on /about, and on /colophon. ## Pages - [Home](https://sinusoidal-history.skylarkcreations.com/): The interactive overlay chart with eight cycle facets, a calibration drawer, and a time-range brush. Hero: "Eight cycles, one axis." - [Methods](https://sinusoidal-history.skylarkcreations.com/methods): Data provenance, transformations, normalization choices, and why Pearson r is a diagnostic and not a test statistic. Per-series source citations and license terms. - [About](https://sinusoidal-history.skylarkcreations.com/about): The argument. Why this exists, why every cycle peaks near now, the eight cycles in this version, the intellectual-honesty disclaimer. - [Colophon](https://sinusoidal-history.skylarkcreations.com/colophon): A note from the maker. How the site was built, what was AI, what was human, the AI-collaboration framing, the convergence problem. - [Poster](https://sinusoidal-history.skylarkcreations.com/poster): A dedicated print-style broadside meant for screenshotting and sharing. Includes a PNG download. - [Embed docs](https://sinusoidal-history.skylarkcreations.com/embed/docs): How to iframe specific cycle facets in a Substack or other host page. ## Plain-markdown content (LLM-friendly) These are the prose pages above, served as raw markdown with permissive CORS so agents and notebooks can fetch them directly. - [/about.md](https://sinusoidal-history.skylarkcreations.com/about.md): The argument and disclaimer, in markdown. - [/methods.md](https://sinusoidal-history.skylarkcreations.com/methods.md): Provenance and methodology, in markdown. - [/colophon.md](https://sinusoidal-history.skylarkcreations.com/colophon.md): Note from the maker, in markdown. ## Data files Each cycle and data series is fully described in the canonical JSON files. CSV data is fetchable cross-origin (CORS `*`). Per-file provenance is in companion `.source.md` files. - [cycles.json](https://github.com/u00dxk2/sinusoidal-history/blob/main/src/data/cycles.json) (in repo): All eight cycles with period, peak year, source citation, peak rationale, and confidence-level classification. - [series.json](https://github.com/u00dxk2/sinusoidal-history/blob/main/src/data/series.json) (in repo): All seven data series with source, URL, license, coverage, and association notes. CSV data files (CORS-enabled, served from the live site): - [/data/dw_nominate.csv](https://sinusoidal-history.skylarkcreations.com/data/dw_nominate.csv) — US House polarization (Voteview, 1879–2023). Provenance: [/data/dw_nominate.source.md](https://sinusoidal-history.skylarkcreations.com/data/dw_nominate.source.md). - [/data/us_tfp_growth.csv](https://sinusoidal-history.skylarkcreations.com/data/us_tfp_growth.csv) — US TFP growth, 5-yr centered rolling, derived from Fernald's `dtfp_util` column (FRBSF, 1948–2025). Provenance: [/data/us_tfp_growth.source.md](https://sinusoidal-history.skylarkcreations.com/data/us_tfp_growth.source.md). - [/data/wid_top1_wealth.csv](https://sinusoidal-history.skylarkcreations.com/data/wid_top1_wealth.csv) — US top-1% wealth share (WID/Saez–Zucman, modern series 1913+, with five pre-1913 spliced points). Provenance: [/data/wid_top1_wealth.source.md](https://sinusoidal-history.skylarkcreations.com/data/wid_top1_wealth.source.md). - [/data/us_world_gdp_share.csv](https://sinusoidal-history.skylarkcreations.com/data/us_world_gdp_share.csv) — US share of world GDP (Maddison Project Database 2023, 1870–2022, rebuilt with regional-aggregate filter and per-country forward-fill). Provenance: [/data/us_world_gdp_share.source.md](https://sinusoidal-history.skylarkcreations.com/data/us_world_gdp_share.source.md). - [/data/vdem_libdem.csv](https://sinusoidal-history.skylarkcreations.com/data/vdem_libdem.csv) — V-Dem liberal-democracy index for the US (V-Dem Institute v16, 1789–2025). Provenance: [/data/vdem_libdem.source.md](https://sinusoidal-history.skylarkcreations.com/data/vdem_libdem.source.md). - [/data/conflict_deaths.csv](https://sinusoidal-history.skylarkcreations.com/data/conflict_deaths.csv) — Deaths in conventional wars per 100k (OWID/Project Mars Lyall 2020, 1800–2011; log1p transform applied at load time). Provenance: [/data/conflict_deaths.source.md](https://sinusoidal-history.skylarkcreations.com/data/conflict_deaths.source.md). - [/data/stimson_policy_mood.csv](https://sinusoidal-history.skylarkcreations.com/data/stimson_policy_mood.csv) — US Policy Mood (Stimson, UNC, 1952–2024 annual; higher = more liberal public preference for domestic policy). Provenance: [/data/stimson_policy_mood.source.md](https://sinusoidal-history.skylarkcreations.com/data/stimson_policy_mood.source.md). ## Build and audit history - [docs/how-this-was-made.md](https://github.com/u00dxk2/sinusoidal-history/blob/main/docs/how-this-was-made.md) — long-form build journal, written for sharing with the maker's friend. - [docs/fact-check-prompt.md](https://github.com/u00dxk2/sinusoidal-history/blob/main/docs/fact-check-prompt.md) — round-1 fact-check prompt. - [docs/fact-check-2026-04-25.md](https://github.com/u00dxk2/sinusoidal-history/blob/main/docs/fact-check-2026-04-25.md) — round-1 fact-check report. - [docs/fact-check-prompt-round-2.md](https://github.com/u00dxk2/sinusoidal-history/blob/main/docs/fact-check-prompt-round-2.md) — round-2 prompt. - [docs/fact-check-2026-04-25-round-2.md](https://github.com/u00dxk2/sinusoidal-history/blob/main/docs/fact-check-2026-04-25-round-2.md) — round-2 report. - [docs/fact-check-prompt-round-3-self-contained.md](https://github.com/u00dxk2/sinusoidal-history/blob/main/docs/fact-check-prompt-round-3-self-contained.md) — round-3 prompt with all content inlined. ## Notes for crawlers and agents - Robots: `*` allowed everywhere, no per-bot restrictions. LLM crawlers (GPTBot, ClaudeBot, PerplexityBot, Google-Extended, etc.) are welcome. - License: site prose is unannotated; data licenses vary per series — see /methods or each `.source.md` file. Cycle-theorist source citations link to the underlying books. - Stability: the site is post-fact-check Phase 11 (round-4 verdicts folded). Notable round-4 corrections: Strauss-Howe "2020 = trough" prose was mathematically false (period 84 + peak 1955 ⇒ trough 1997, next peak 2039, 2020 on rising arm at cos ≈ +0.15) and has been rewritten; Pearson "linearity" bullet replaced with phase-sensitivity (r = cos Δφ for same-period sinusoids); TFP display range corrected to 1948–present (was incorrectly stated as ~1950); Maddison forward-fill pre-1950 bias surfaced; Dalio anchor-from-different-cycle mismatch acknowledged; WID pre-1913 splice provenance disentangled from Saez–Zucman 2016; Project Mars 2010 = 0 explained as definitional artifact. Schlesinger Jr. cycle + Stimson Policy Mood pairing added in Phase 10. Treat any older snapshot as superseded. - Contact: build journal lists the maker; bugs and corrections welcome through GitHub issues.