Dimensionality critically governs correlated states, often inducing emergent ground states in reduced dimensions. While ${\mathrm{VSe}}_2$ has been studied extensively, its monolayer ground state remains controversial. Here, we resolve these issues by investigating the thickness-dependent evolution of charge density waves (CDWs) and magnetism in ${\mathrm{VSe}}_2$. Using angle-resolved photoemission spectroscopy, we observe pronounced temperature-dependent band reconstruction uniquely emerging in bilayer and monolayer ${\mathrm{VSe}}_2$, in sharp contrast to bulk and multilayer ${\mathrm{VSe}}_2$. While a $\sqrt{3}\times \sqrt{7}$ CDW accounts for the reconstructed band topology, it fails to explain the global suppression of spectral weight at low temperature. Instead, DFT calculations suggest that a coupled $\sqrt{3}\times \sqrt{7}$ spin density wave $\left(\mathrm{SDW}\right)+\mathrm{CDW}$ state can quantitatively account for all key experimental observations. These results are consistent with a thickness-driven crossover to a coupled $\mathrm{SDW}+\mathrm{CDW}$ state, establishing ${\mathrm{VSe}}_2$ as a tunable platform for exploring intertwined spin-charge orders in two-dimensional quantum materials.

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• Antiferromagnetism
• Band gap
• Charge density waves
• Electronic structure
• Magnetic phase transitions
• Magnetism
• Nesting
• Phase diagrams
• Phase transitions
• 2-dimensional systems
• Antiferromagnets
• Magnetic thin films
• Transition metal dichalcogenides
• Ultrathin films
• Angle-resolved photoemission spectroscopy
• Density functional theory
• First-principles calculations
• Methods in magnetism
• Molecular beam epitaxy