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tokens: population thought to result from satellite galaxy accretion (e.g. Forbes Bridges 2010 ; Leaman, VandenBerg Mendel 2013 ). These results suggest that the detailed age–metallicity distribution of GCs may be used to infer the accretion history of the host galaxy. The key ingredient enabling us to extract the wide range of information encoded in the Galactic GC population is the E-MOSAICS 1 project (Pfeffer et al. 2018 ; Kruijssen et al. 2019 ). Cluster formation and disruption are well known to depend on the local environmental conditions within galaxies (see recent reviews by Kruijssen 2014 ; Forbes et al. 2018 ). Modelling the co-formation and co-evolution of GC populations and their host galaxies thus requires following the spatial and kinematic phase-space distributions of the cluster populations self-consistently in their cosmological context. This prohibits the use of models based on semi-analytic or particle tagging techniques. Instead, E-MOSAICS self-consistently couples environmentally dependent sub-grid models for the formation, evolution, and tidal disruption of stellar clusters (MOSAICS, Kruijssen et al. 2011 , 2012 ; Pfeffer et al. 2018 ) to the locally resolved baryonic conditions obtained with the state-of-the-art cosmological galaxy formation model EAGLE (Schaye et al. 2015 ; Crain et al. 2015 ). The initial set of 25 hydrodynamical cosmological zoom-in simulations of Milky Way-mass galaxies allows us to follow the co-formation and co-evolution of galaxies and their GC populations. Specifically, we show in Kruijssen et al. ( 2019 ) that the distribution of GCs in age–metallicity space is a sensitive probe of the host galaxy’s formation and assembly history. The GC age–metallicity distributions obtained in E-MOSAICS exhibit strong galaxy-to-galaxy variations, resulting from differences in their evolutionary histories. By correlating several metrics describing the GC age–metallicity distributions of the 25 simulated galaxies with quantities describing their formation and assembly histories (such as halo properties, formation and assembly redshifts, stellar mass assembly time-scales, numbers of major and minor mergers, redshift distribution of mergers), we identify a set of 20 correlations with high statistical significance. These correlations show that the GC age–metallicity distribution is a sensitive probe of the host galaxy’s stellar mass growth, metal enrichment, and minor merger history. Moreover, it is shown that the mass dependence of galaxy evolution in age–metallicity space enables the use of individual GCs to infer the masses and metallicities of their natal galaxies as a function of redshift. We demonstrate that this can be used to reconstruct the merger tree of the host galaxy. Applying any of these individual results to the GC population of the Milky Way may already significantly increase our understanding of its formation and assembly history. In this paper, we take the comprehensive approach of employing the full