This study examined Kenya's national security threats resulting from the withdrawal of the Kenya Defence Forces (KDF) from the African Union Mission in Somalia (AMISOM). This was in light of previous Peace Support Operation Transitions (PSO) in Iraq and Afghanistan, where regional instability resulted from troop withdrawals. Therefore, it analysed the impact of PSO experiences on national security, aiming to identify potential threats to the national security of Troop-Contributing Countries (TCC) resulting from PSO involvement. The study was a descriptive survey design, and it adopted a mixed-methods approach. The sample size for the study was 400 respondents and 49 key informants. The survey was informed by functionalist theory and strategic theory. Kenyan border counties are predisposed to the security effects of the KDF transition from AMISOM. The study's findings indicated a complex security landscape; that is, weak Somali security forces, insufficient funding for the transition, a short time frame, and the likelihood of a resurgent Al-Shabaab all present significant threats to Kenya's national security. These issues are exacerbated by increased border security problems, such as smuggling and unresolved territorial conflicts. However, the studies indicated that Kenya could mitigate these risks. Influencing the Security Transition Plan (STP) to prioritise strong border security measures can strengthen Kenya's defences. Strengthening the Jubaland buffer zone and helping Somalia's disarmament, demobilisation, and reintegration (DDR) initiatives can help weaken terrorist organisations. Furthermore, efforts in Kenya's border counties' socioeconomic development can reduce the attraction to extreme ideas. Implementing comprehensive border security measures provides an additional avenue for improving overall security. According to the analysis, AMISOM's transition represents a complicated security tightrope walk for Kenya. To counteract the problem, Kenya must address the highlighted dangers while capitalising on existing opportunities. Analysis of Variance (ANOVA) indicated an F statistic of 139.893 and a p value of 0.000<0.05, implying that the transition of the Kenyan contingent in the African Union mission in Somalia significantly predicts Kenya’s national security. The regression weights model showed that the transition of the Kenyan contingent in the African Union mission in Somalia had a negative and significant influence on Kenya’s national security (β = -0.368, P =.000<.05). Recommendations include actively shaping the STP, strengthening the Jubaland buffer zone, and stationing enough security personnel along the border. Promoting bilateral and multilateral engagement with Somalia is critical for resolving lingering concerns and maintaining regional stability. By taking these steps, Kenya can protect its national security throughout AMISOM's handover.