"power expand" is a correct and usable phrase in written English.
You can use it to describe an increase in power or influence of something. For example, "The company's efforts to power expand in the international market proved successful."
As American power expanded abroad, liberty grew at home.
Parthian military, political, and economic power expanded considerably following the accession of Mithradates I.
The Fugitive Slave Act, the Kansas-Nebraska Act, the Dred Scott decision -- all suggested to them that abolitionist politics was failing, the Slave Power expanding.
But he also grew increasingly despotic and corrupt as his power expanded, turning the urban elite's distaste for him into outright loathing.
At the least, his exercise of administrative power expanded and cemented a domestic legacy that now rivals Lyndon B. Johnson's Great Society in reach and scope.
Politicians were happy to use the threat of al-Qa'ida to persuade people that their civil liberties should be restricted and state power expanded, but they spent surprisingly little time calculating the most effective practical means to combat the movement.
China, the only major power expanding its arsenal, likely has 240 to 300 nuclear weapons in its arsenal, but experts say no more than 50 are capable of hitting the United States.
"The website's overnight success brought instant fame to its principal architects, but as their power expanded across the globe, Daniel grew increasingly disillusioned with Julian's questionable tactics and ethics.
Paddy Power expanded its High Street network, opening 41 outlets in the UK last year to bring its total to 165.
As wireless power expands its influence, the Internet of Things will change the way we operate and carry on our daily lives.
