The swift Islamic expansion across the Mediterranean, culminating in the 8th-century CE conquest of the Iberian Peninsula and the end of the Visigothic Kingdom, is a pivotal event in history. While economic, social, and political factors played undeniable roles, the influence of climate change on this transition remains relatively unexplored. This study aims to investigate the potential contribution of drought to the instability that facilitated the Islamic conquest. Recent research increasingly emphasizes the impact of climate on historical crises in the Mediterranean, particularly concerning the Dark Age Cold Period and its link to events like the Justinian Plague and rural settlement crises. The Visigothic Kingdom, lasting approximately 300 years (5th–8th centuries CE), experienced a period of internal strife and fragmentation before the Umayyad Caliphate's conquest. While archaeological evidence illuminates Visigothic farming strategies and social organization, the precise causes of the kingdom's rapid fall remain debated. This paper specifically addresses the largely uninvestigated hypothesis that climate change, in the form of widespread and persistent drought, served as a significant catalyst for the Islamic expansion from North Africa into Iberia. The scarcity of high-resolution paleoclimate records and studies focusing on the impact of climate change on early medieval kingdoms has hindered previous assessments of this hypothesis. Understanding the interplay between climate and societal shifts in this crucial period can offer valuable insights into the resilience and vulnerability of past societies to environmental change, as well as offer parallels for contemporary challenges.

Existing scholarship on the Visigothic Kingdom's decline and the Islamic conquest of Iberia largely focuses on political and social factors, such as internal conflicts, military campaigns, and religious conversions. However, the role of climate change, particularly drought, has received limited attention. Studies on the Dark Age Cold Period and its correlation with the Justinian plague and socioeconomic disruptions in Europe offer a framework for investigating climate's influence on this period. Existing Holocene paleoclimatic studies in the Mediterranean region at decadal-to-centennial scales highlight precipitation as the primary climate factor affecting environmental variability. These studies point to the significant impact of precipitation fluctuations on population dynamics and human settlements in the region. Nevertheless, a comprehensive analysis incorporating high-resolution paleoclimate data, archaeological findings, and historical records specifically focusing on the period of the Visigothic Kingdom's collapse and the subsequent Islamic expansion has been lacking. The present study bridges this gap.

This research employs a multi-proxy approach to reconstruct past climate conditions in the Iberian Peninsula and Morocco during the period from the mid-5th to the mid-10th centuries CE (450–950 CE). The core of the methodology involves creating a high-resolution pollen stack, drawing upon 107 pollen records from Iberia and Morocco, obtained from the Neotoma database, European Pollen Database, and direct contact with researchers. The analysis focuses on *Artemisia* and other xerophytic pollen taxa as indicators of aridity. These pollen data are complemented by other paleohydrological data, including isotopic analyses of speleothems from caves in northern Morocco and Spain (Chaara cave, Cobre, Kaite, and Mayor caves). Speleothem records offer additional insights into regional paleoclimate patterns. The correlation between these pollen and speleothem records is analyzed using Pearson's correlation coefficient to assess the consistency of aridity indicators. To identify statistically significant drought periods, the researchers applied the Scale-normalized Significant Zero-crossing (SnSiZer) statistical analysis to the stacked *Artemisia* pollen record. The results of the SnSiZer analysis are then compared with available historical and archaeological evidence. Historical sources, including chronicles and accounts from various authors, are compiled to document political events, famines, plagues, and societal upheaval. Archaeological data from rural and urban settlements are reviewed to assess the impact of climate on settlement patterns, agricultural practices, and socioeconomic stability. The study integrates information from various sources to evaluate the potential influence of drought on the Visigothic Kingdom's instability and the subsequent Islamic expansion. The age chronologies for the pollen records are obtained from the databases, incorporating the original chronologies and those produced by the MADCAP working group of the EPD. The researchers also performed a calibration using the EMPDv2 and WorldClimv2.1 data to evaluate the relationship between *Artemisia* percentages and precipitation levels. Data normalization (z-score normalization) is conducted on the fossil *Artemisia* and xerophyte data before stacking and averaging to facilitate comparison with other paleoclimatic records. The SnSiZer analysis employs scale-normalized derivatives to identify statistically significant increases and decreases in *Artemisia* abundance, indicating aridity trends. Additional paleoclimate reconstructions, such as the NAO index and Total Solar Irradiance (TSI) data, are incorporated to explore potential climate mechanisms driving the observed drought events.

The study identifies four statistically significant periods of extreme drought between the mid-5th and mid-10th centuries CE (450–950 CE) based on the SnSiZer analysis of the stacked *Artemisia* pollen data: 545–570 CE, 695–725 CE, 755–770 CE, and 900–935 CE. These findings are corroborated by independent paleoclimate proxies, such as speleothem δ18O and δ13C records from Morocco and Spain. The maximum drought intensity of the last 5000 years occurred during the period 695–725 CE, as indicated by the highest *Artemisia* values. The positive correlation between *Artemisia* abundance and speleothem isotopic data suggests a link between increased aridity and decreased precipitation. The 545–570 CE drought coincides with the onset of the Late Antique Little Ice Age (LALIA), possibly triggered by volcanic eruptions, which led to crop failure, famine, and the spread of the Justinian plague. The 695–725 CE drought, the most severe of the four, coincides with the Visigothic Kingdom's political and social crisis, characterized by internal conflict, famine, plague, and ultimately, the Muslim invasion of 711 CE. The 755–770 CE drought corresponds to early instability within the newly established Umayyad Caliphate in Iberia, including Berber uprisings and famines. The 900–935 CE drought coincides with the first *fitna* (Muslim civil war) within the Emirate of Córdoba. The study notes that while human activity might influence vegetation cover, the large number of pollen records used minimizes the impact of localized human effects, supporting the robustness of the findings. Furthermore, comparisons with broader paleoclimate reconstructions, such as NAO index and TSI, suggest links between solar activity, atmospheric circulation patterns, and the occurrence of drought events in the western Mediterranean.

The findings strongly suggest that the identified drought periods significantly contributed to the instability of both the Visigothic Kingdom and the subsequent Muslim rule in Iberia. The primarily agriculture-based economies of these early medieval kingdoms were highly vulnerable to prolonged drought, leading to food shortages, famines, and social unrest. This created a weakened political climate ripe for conquest and internal conflict. The coincidence of severe droughts with periods of political turmoil and societal disruption strongly supports the hypothesis that climate played a crucial role in shaping this historical transition. While the political and social factors were undoubtedly important drivers of these events, the study's results demonstrate the substantial influence of environmental stress, particularly persistent and severe droughts, as a significant exacerbating factor. The study highlights the importance of incorporating long-term environmental variability in the interpretations of historical events and underlines the vulnerability of agrarian societies to climatic shifts. The study's multi-proxy approach enhances the reliability of the findings, minimizing the impact of potential biases in individual data sources. The results provide a new perspective on the complex interplay of environmental and socio-political factors in shaping historical transitions.

This study demonstrates the significant role of drought as a contributing factor to the decline of the Visigothic Kingdom and subsequent sociopolitical instability in al-Andalus. The four identified periods of extreme drought, corroborated by multiple paleoclimate proxies and historical records, created conditions of widespread famine, disease, and social unrest, weakening these kingdoms and facilitating their transformation. This research highlights the urgent need for incorporating long-term environmental dynamics into historical analyses, especially considering the increasing vulnerability of modern societies to climate change. Further research could explore in detail the specific adaptive strategies employed by various communities in response to these droughts and the long-term consequences of these events on societal development and cultural exchange. Furthermore, expanding the analysis to include a broader range of paleoclimate data and investigating analogous situations in other regions could offer a wider perspective on climate's influence on historical processes.

While the study utilizes a comprehensive dataset, potential limitations include the inherent uncertainties in age modeling of paleoclimate records. The analysis relies on *Artemisia* pollen as a key indicator of aridity. While this is a widely accepted proxy, other factors, beyond climate, could influence *Artemisia*'s abundance, including human impact on land use and vegetation. The resolution of the historical records used is sometimes lower than that of the paleoclimate data, limiting the precise correlation between events. The study focuses primarily on the Iberian Peninsula and North Africa; extending the analysis to include other parts of the Mediterranean could provide a broader understanding of regional climate patterns and their impact.