"join their efforts" is a correct and usable phrase in written English.
You can use it when speaking about combining the efforts of two or more people to work towards a common goal. For example, "The activists decided to join their efforts to raise awareness about climate change."
In the holy Koran, human beings are invited to join their efforts in, and means solidarity, which can be translated into co-operation to do good.
Coaches, players, health professionals, and researchers should join their efforts to investigate the effect on injury incidence and injury pattern associated with the duration and content of the preseason period, and the number of friendly matches held during preseason.
Each of these new clearinghouses had to persuade big banks to join their efforts, and they doled out membership on their risk committees, which is where trading rules are written, as an incentive.
In the framework of Mars exploration, particularly for missions dedicated to the search for life or for traces of ancient forms of life, NASA and CNES have decided to join their efforts in order to build a Mars sample return mission.
The same is true of Pakistan's Islamist movements, which emerged out of a diverse set of ideological traditions, yet nonetheless have managed at times to join their efforts in the political domain.
Gun control activists speaking at a Yale School of Public Health forum this week urged public health professionals to join their efforts in combating the pervasive gun violence that has become a major public health threat across the country.
The Eazel team persuaded Susan Kare, a graphic artist who designed icons for the original Macintosh and also for Microsoft, to join their effort.
The Yale economist William Nordhaus has recently analyzed one way of doing this — forming a trade club, in which members adopt an emission-reduction policy and impose tariffs on countries that refuse to join their effort to limit climate change.
At a news conference on Sunday, Ammon Bundy said his group had not heard from law enforcement since taking over the unoccupied site and urged other citizens from across the country to join their effort.
Talking to reporters gathered at the entrance to the refuge property, Bundy said his group had not heard from law enforcement since taking over the unoccupied site and urged other citizens from across the country to join their effort.
Zendesk learned about the filing after it was publicized last night and contacted the companies involved to join their effort, a source said.
