In recent years, it has become clear that the dynamics and secular evolution of galaxies is largely affected by their local environment:(possibly dark) subhalos in the whole mass range from $10^7$ up to $10^{10}$ solar masses are subject to halo-induced dynamical friction leading to continuous matter infall into larger galaxies. A prominent example is the Milky Way, which currently exhibits strong tidal interactions with relatively massive satellite galaxies such as Sagittarius and the Magelanic Clouds, and a larger number of (possibly yet undetected) lighter sub-halos. The talk will focus on results obtained via a new particle-mesh N-body code (MAIN: presented in Kyziropoulos et al., MNRAS, 2016). We simulate the generation of spiral structure in a Milky-way-type galactic disc via successive flybies of a companion galaxy. We will discuss the main dynamical features of such an interaction. We will also refer to constrains that such sort of studies suggest in relation to observational campaigns aiming to determine the dynamical history and/or current and past close-environment interactions of our own Galaxy.