Since 2007-2008, Africa has become the center of estate-driven land acquisitions to produce feed, food, biofuels, and fiber for the international market, which has raised contested narratives of African development and critical sustainability challenges. This is the case for the “Sisal Belt” of Kilosa in Tanzania, where Chinese firms resurrected former colonial sisal estates and generated wage labor for adjacent farmers, changing local agrarian structures with significant implications for smallholder cultivation and the environment at large. Land system science aims to understand the land use and land cover dynamics as a coupled social-environmental system, focusing on the spatiotemporal patterns and the underlying socioeconomic and environmental drivers, impacts, and feedbacks of land system change. Following this interest, this dissertation uses three empirical studies to understand the processes of land system transformation in the sisal belt region and examine the consequences of the co-development by the estate and smallholder agriculture. The first study conducts long-term time series land-cover mapping and remote sensing analysis via Google Earth Engine to detect land changes and their spatial and socio-economic linkages to estate operations and smallholder livelihoods. The second study applies agent-based modeling to assess the distinctions among smallholder households in land-use and livelihood decision-making mechanisms when confronting estate wage labor and cash crop opportunities. The third study quantifies and identifies critical tradeoffs between carbon, water services, and the outcomes of commodity economies based on distinct future scenarios of development visions and estate-smallholder relationships up to the year 2030. The findings of these studies advance the understanding of the human-environmental conditions of estate and smallholders in Tanzania under the African land rush underway, which is consistent with the interest of land system and sustainability sciences. The policy implications drawn from this dissertation suggest that the primary land users and decision-makers should recognize the history and realities of the existing agrarian systems and engage in creative ways that serve the estate and the smallholder, including improving smallholder production and localizing estate operations. Such policies should be informed by assessments of changes in the environment and its services and be guided by local knowledge, needs, and future aspirations.