  Thinning crystalline materials to two dimensions (2D) creates a rich
playground for electronic phases, including charge, spin, superconducting and
topological order. Bulk materials hosting charge density waves (CDWs), when
reduced to ultrathin films, have shown CDW enhancement and tunability. However,
charge order confined to only 2D remains elusive. Here we report a distinct
charge ordered state emerging in the monolayer limit of 1T-VSe$_2$. Systematic
scanning tunneling microscopy experiments reveal that bilayer VSe$_2$ largely
retains the bulk electronic structure, hosting a tri-directional CDW. However,
monolayer VSe$_2$ exhibits a dimensional crossover, hosting two CDWs with
distinct wavelengths. Electronic structure calculations reveal that while one
CDW is bulk-like and arises from the well-known Peierls mechanism, the other is
decidedly unconventional. The observed CDW-lattice decoupling and the emergence
of a flat band suggest that the new CDW arises from enhanced electron-electron
interactions in the 2D limit. These findings establish monolayer-VSe$_2$ as the
first host of coexisting charge orders with distinct origins, opening the door
to tailoring electronic phenomena via emergent interactions in 2D materials.
