Texas Legal Guide (texaslegalguide.com) is currently under construction.
This page is available for comment and discussion regarding the page Article IV, Section 7 of the Texas Constitution.
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The existence of martial law depends fundamentally on necessity. It does not supersede the civil autharity, but finding that authority destroyed by insurrection it establishes a martial government to avoid the anarchy which would otherwise be inevitable. The powerlessness of the civil arm of government is therefore a condition precedent to the exercise of military authority.
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It follows that where the courts are open and their process unobstructed the arrest and trial of persons by military authority is unauthorized.
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https://lrl.texas.gov/scanned/Senatejournals/14/S_14_2.pdf#page=19
governor's 1875 explanation of his limited powers