If you’re going to do it, do it right

1992: American marines land in Somalia

From the BBC On This Day page for today, which links to a story about the battle in Mogadishu the following year which includes:

Defence Secretary Les Aspin has stated that US forces will not remain in Somalia longer than necessary. But speaking on CBS he cautioned:

“It’s important not to withdraw in a way that, 18 months later, people will say, ‘Well, it never made any difference’.”

Osama bin Laden has said specifically that the way way US troops were withdrawn after that battle demonstrated to him that terror attacks against America would bring about the results he wanted, so I’d say it definitely made a difference.