Global conventions play a crucial role in the international community's efforts to combat terrorism by providing a legal framework for cooperation, but their efficacy is multifaceted and subject to various challenges.

Strengths and Contributions:

1. Legal Framework: These conventions establish a common legal basis for states to criminalize terrorist acts, prosecute offenders, and cooperate on extradition. Key examples include the 1999 International Convention for the Suppression of the Financing of Terrorism, the 1979 International Convention against the Taking of Hostages, and various conventions related to aviation security. These instruments define specific terrorist acts, obligate states to take preventive measures, and ensure that perpetrators do not find safe haven.
2. International Cooperation: Conventions facilitate information sharing, intelligence exchange, and mutual legal assistance among states. This is vital for tracking terrorist networks, disrupting their operations, and bringing them to justice across borders.
3. Universal Jurisdiction: Many conventions incorporate the principle of 'aut dedere aut judicare' (extradite or prosecute), compelling states to either extradite suspected terrorists to a country with jurisdiction or prosecute them domestically, thereby closing potential legal loopholes.
4. Asset Freezing and Sanctions: Conventions, particularly those related to financing, enable states to freeze assets of terrorist organizations and individuals, cutting off their financial lifelines.
5. Normative Impact: They help to build a global consensus against terrorism, stigmatizing it as an unacceptable act and fostering a shared understanding of the need for collective action.

Weaknesses and Challenges:

1. Lack of a Universal Definition: A significant hurdle is the absence of a universally agreed-upon definition of terrorism. This often leads to political disagreements, with states sometimes distinguishing between 'terrorists' and 'freedom fighters,' hindering unified action.
2. Implementation Gaps: While many states ratify conventions, their effective implementation varies widely due to differences in legal systems, political will, resource constraints, and capacity.
3. State Sponsorship and Support: Some states are accused of directly or indirectly supporting terrorist groups, undermining the spirit and letter of these conventions.
4. Evolving Nature of Terrorism: Terrorism is dynamic, adapting to new technologies and methods (e.g., cyberterrorism, lone-wolf attacks, use of social media for radicalization). Conventions often struggle to keep pace with these evolving threats.
5. Human Rights Concerns: Counter-terrorism measures, sometimes justified under the umbrella of conventions, can lead to human rights abuses, raising concerns about due process, torture, and arbitrary detention.
6. Political Will and Sovereignty: States may prioritize national sovereignty or political interests over full compliance, especially when it involves sensitive intelligence or extradition of their own citizens.

Conclusion: Global conventions are indispensable tools in the fight against international terrorism. They provide the essential legal and normative architecture for states to cooperate. However, their efficacy is limited by political disagreements, implementation challenges, the evolving nature of the threat, and the lack of a universal definition. For these conventions to be truly effective, there is a continuous need for stronger political commitment, enhanced capacity building, greater transparency, and a willingness to overcome nationalistic interests in favor of collective security, while upholding human rights principles.