So little pain taken… talk about total BS. I’d say Kansas was painful. I’d say the debates over Missouri, over The Fugitive Slave Act, over popular soverenty, or the admission of Texas, or the Wilmount Proviso, or the southern filibusters into Mexico and Central America, or the desire to annex Cuba or Dred Scott… I’d say they were are part of very painful preview of the war.
Your British journalist didn’t know what the hell he was talking about.
Firstly he was talking about the New Mexico territory - ie New Mexico and Arizona. Next, individual filibusters into Mexico or Central America did not have popular support and were not an expression of the political will of the people of the South or indeed of the whole country. Several of them were much more motivated nationalist sentiments than concerns over slavery. The Fugitive Slave Act and the constitutional fugitive slave provision weren't really about the expansion of slavery.
If the expansion of slavery were truly desired for its own sake or because of economic reasons, why were the Southern states perfectly content to secede without claiming any of the Western territory? The very act of secession meant giving up any chance to spread slavery there. That would hardly seem like a reasonable solution if their real concern were spreading slavery. If however they were far more motivated by a power struggle over federal economic policy in Washington DC then suddenly it would all make sense.....