The phrase "act alone if" is correct and usable in written English.
It can be used in contexts where you are discussing the conditions under which someone may choose to act independently.
Example: "You may act alone if you believe it is in the best interest of the project."
Alternatives: "proceed independently if" or "take action alone if".
Yet he also made clear that the United States would act alone if the United Nations hesitated.
But the Bush administration has always made it clear it is prepared to act alone if necessary.
This matters to Germany; although it will act alone if necessary, it still fears the appearance of imposing its will unilaterally.
Few foreign volunteers make their way to the battlefronts of the Middle East alone, and few are likely to act alone if they ever make it home.
By presenting Moscow with a counter-incentive, threatening to act alone if Moscow does not use its influence to bring an end to the conflict, the United States could demonstrate that it is serious about engagement.
It says America will always act, alone if necessary, to protect our people and our allies; but on issues of global concern, we will mobilise the world to work with us, and make sure other countries pull their own weight".
Stepfathers act alone in 5%%.
Yet none of the publishers seemed to think that they could act alone, and if they presented a unified demand to Amazon they risked being charged with price-fixing and collusion.
He made it clear that America, in the end, would act alone against Iraq if need be.
(That act alone makes us wonder if Sunny is indeed crazy.) Like "Twin Falls, Idaho," the first film by Michael and Mark Polish, "Jackpot" -- Michael directed and wrote the script with Mark -- is redolent of desperation, delusion and kitsch.
Where America's security and interests are not directly threatened but conscience urges the country to act, such as when a dictator is killing a large number of his own citizens, America should not act alone and only use force if there is a good chance of success.
