在过去的60年里，pta有了惊人的增长。有许多州从一开始就是pta的一部分，现在正在做出创新的安排。在国际政治经济中，PTAs的关键特征有所增加(Missios, Saggi和Yildiz, 2016)。这背后的主要原因是，许多国家通过增加其他成员来扩大。一些pta增长背后的原因是什么?为什么其他的pta没有扩张?在这个重要的问题上，只有很少的重点被强调(Seidmann, 2009)。本文所关注的双边贸易协定和轮辐协议并没有增长。
另一方面，多边贸易协定的规模也在不断扩大。对于新的成员，可能作出的一些安排是开放的，涉及贸易和所有成员的分配是相同的。在新州成为pta的一部分后，它们按时间顺序排列。未来，PTAs仍希望其他成员加入。与此同时，PTA希望在全球范围内发展(Lee，罗兰-霍尔斯特，van der Mensbrugghe, 2004)。一些事实表明，更大的市场有可能增长，而不是较小的安排。人们注意到，太平洋贸易协定的重点在于使新成员国成为其成员，而这一重点是建立在这些成员国在政治和经济上的一致性基础上的。需要与pta现有参与者相似的地方如下:市场规模、政体类型、贸易开放与政治统一性(Ghosh and Yamarik, 2004)。在本文的帮助下，也为今后的研究提供了机会。比如，目前只重视pta，并没有太多的努力去了解国际机构成长的原因(Bagwell and Staiger, 2001)。
为了确定本分析的结果仅限于pta，还需要进一步的研究。此外，未来的研究将解释国际机构大幅增长的原因(Seidmann, 2009)。本文分析了影响PTA在全球范围内发展的更多因素，包括PTA与国家之间的战略互动、成员的规模分布以及PTA上一次扩张的时间长短。此外，双边贸易协定很少扩大的发现并不局限于经济机构(Chang and Xiao, 2015)。
There has been an incredible growth of PTAs in the last sixty years. There are many states, which are part of PTAs from the beginning and now make innovative arrangements. In the international political economy the crucial features of PTAs has increased (Missios, Saggi and Yildiz, 2016). The main reason behind it is that many of states have expanded by adding other members. What is the reason behind the growth of some of the PTAs and why other PTAs do not expand? On this important issue, only little focus has been emphasized (Seidmann, 2009). There was no growth of bilateral PTAs and hub and spoke agreement, which this paper has focused upon.
On the other hand, PTAs, which are multilateral, are enlarging. To the new members some arrangements, which are likely to be made, are open with respect to trade and the distribution of all the members is homogenous. After new states became part of the PTAs they exhibits chronological grouping. PTAs still wants other to make its member in the future. At the same time, PTA wants to grow globally (Lee, Roland-Holst and van der Mensbrugghe, 2004). Some facts have been shown which shows that instead of smaller arrangements there are chances for the growth of larger markets. It has been noticed that the focus of the PTAs for making new states its member is based upon their political and economical consistency of previous members. The points which needs to be similar to that of existing participants of PTAs are as follow; market size, regime type, trade openness and political uniformity (Ghosh and Yamarik, 2004). With the help of this paper, there are chances for the researches in future also. Like, at present the more emphasize is given to only PTAs and not many efforts are applied for knowing the reasons for the growth of international institution (Bagwell and Staiger, 2001).
For determining the outcome of this analysis are restricted to PTAs there is need for future research. In addition, future research would explain the reason behind the large growth of international institution (Seidmann, 2009). This paper have analysed more factors which would help to guide the growth of those institution which are spread all over the world, which includes strategic interaction among PTAs and among states, the size distribution of members, and the length of time since a PTA last expanded. Moreover, the finding that bilateral PTAs rarely expand is not limited to economic institutions (Chang and Xiao, 2015).