“Community effect” conventionally describes differentiation occurring only when enough cells help their local (micrometers-scale) neighbors differentiate. Although new community effects are being uncovered for myriad differentiations, macroscopic-scale community effects - fates of millions of cells all entangled across centimeters - remain elusive. We found that differentiating mouse Embryonic Stem (ES) cells that are scattered as individuals over many centimeters form one macroscopic entity via long-range communications. The macroscopic population avoids extinction only if its centimeter-scale density is above a threshold value. Single-cell-level measurements, transcriptomics, and mathematical modeling revealed that this “global community effect” occurs because differentiating ES-cell populations secrete, accumulate, and sense survival-promoting factors, including FGF4, that diffuse over many millimeters and activate Yap1-induced survival mechanisms. Only above-threshold-density populations accumulate above-threshold-concentrations of factors required to survive. We thus uncovered a previously overlooked, large-scale cooperation that underlies ES-cell differentiation. Tuning such large-scale cooperation may enable constructions of macroscopic, synthetic multicellular structures.