Will (potential) Trump trade wars usher end of secular bull market?

The current secular bull market started March 9, 2009. It is approaching 16 years. Depending on your source, the average secular bull market is 16-17 years, and average secular bear market is ~12. The durations aren't fixed, and vary by as much as 10 years.

If trade wars start in earnest, one possible outcome is a severe economic contraction, as costs skyrocket and demand subsides. This would put strain on the weaknesses in the system, which could exacerbate the problem (i.e. post-covid commercial real estate).

My question is, for those more informed, what factors contributed to secular bear markets in the past? Do we face similar headwinds today? Why or why not?

Edit: A secular market refers to a long-term trend in the financial markets that lasts for years or even decades, driven by fundamental economic, demographic, or technological shifts. It lasts multiple shorter bull and bear market cycles.

Chart explaining it - https://d1-invdn-com.akamaized.net/content/picde5e957ae5545507aa034839832bafa5.gif

Edit 2: lots of confusion on "secular market". It's a trend of trends. * Great depression took 25 years before market set new highs * Stagflation took 16 years * Dotcom bubble took 13 years

Unless history does not repeat itself (hint: it does), there will be another similar period of stock valuations remaining stagnant for an extended period of time.