The threat of raids into Yorkshire from Scotland
1709 (ref: WYL1352/A1/8/34/245)
Napoleonic invasion was considered a real threat.
April 1798 Pontefract Quarter Sessions (ref:QS1/137/4) includes indictments for seditious libel re favouring invasion by France, and by Bonapart;demand for accounts of monies spent in raising troops by W.Riding; resolutions re raising of extra Volunteer Corps to resist invasion anywhere in Britain.
World War II invasion