The ability to engineer and control microstructures and interfaces represents a real challenge for advanced ceramics, where structural reliability enormously affects the final product's functionality. The main objective for designing and fabricating novel, strong nanocomposite ceramics with superior damage tolerance and improved toughness relies on combining the latest-generation techniques for the multi-scale and correlative characterization of crack propagation mechanisms. Recent literature shows that it is possible to fabricate a new generation of ceramic materials with simultaneous high strength and toughness. Some studies have shown that CeTZP can be an up-and-coming solution for developing strong yet ductile nanocomposite ceramics with potential applications in the biomedical and aerospace fields. However, understanding such specific mechanisms and their interplay to provide such an extraordinary combination of properties is not yet achieved. This work will use multi-technique mechanical characterization methods (e.g., macro-bending combined with electron microscopy and micro pillar-splitting) to elucidate the correlations between materials' microstructure and crack nucleation and propagation mechanisms. Indeed, the crack propagation resistance in ceria-stabilized zirconia and nanocomposite ceria-stabilized zirconia samples (i.e., alumina and strontium aluminate nanospheres and nanoplatelets doped) is assessed as a function of the activation volume for the toughening mechanisms (i.e., phase transformation and crack deflection) and ceria dopant concentration, implementing novel ex-situ micro-pillar splitting experiments of increasingly different diameters. The deviations from experimental macro-fracturing values are investigated in correlation with the latest high-speed nanoindentation machine learning deconvolution of mechanical properties, Raman spectroscopy for gallium damage assessment within the micro-structures, and Focused Ion Beam residual stresses measurements. While a non-significative extension of the damaged area exists for the milling process, indeed, a strong dependence upon the tested pillar diameter is evidenced for ceria stabilized-ceramics of ~60% (from  to ) also changing the fracturing mechanisms. The dependence is reported as reproducible over the several fabricated micro-specimens evidencing a relationship not just with the probing volume but more predominantly with the activation energy for phase transformation and crack deflection. This discrepancy is highlighted when secondary phases are added to the composite ceramic. Low compressive residual stresses (~60 MPa) have also been measured, which could hinder and delay the transformation mechanisms.