The central state, though often very rich and very populous, was intrinsically fragile, since the development of new international trade routes could undermine the monetary base and erode state power, as occurred when European seafarers circumvented Middle Eastern merchants after Vasco da Gama's voyage around Africa in the late fifteenth-century opened up a southern route.
这个句子很长，需要耐心读完，先读一遍之后找出生词。
本句的难点在于一是长度，二是生词有些多。
一节一节地理解：
The central state，中央的州（或者国家）；
though often very rich and very populous，though 表示转折，虽然非常富有且人口众多；
was intrinsically fragile，两个生词，（本质上地；脆弱的），本质上是很脆弱的；
since the development of new international trade routes，看到since首先想到的是原因状语，因为新的国际贸易路线的发展；
could undermine the monetary base and erode state power, undermine，monetary，erode三个生词：削弱；货币的金融的；侵蚀，削弱；）
as occurred，正当（when引导的定语从句）出现；
when European seafarers circumvented Middle Eastern merchants，当欧洲海员们避开中东商人们；
after Vasco da Gama's voyage around Africa in the late fifteenth-century opened up a southern route.
这一部分有些长，先不看around Africa in the late fifteenth-century ，这些都是voyage的定语修饰。主干是：V.D.A的航行开辟了南方路线；修饰成分：15世纪末绕非洲的。
每次把句子这么一拆分，就感觉句子的意思是非常明确了，平时练习的次数多，练习的句子多了，就能做到立马领会句子的含义，这就提高了阅读速度。
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